Read Ebook: The Flow of Time in the Connecticut Valley: Geological Imprints by Bain George W George William Meyerhoff Howard A Howard Augustus

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Near the northern terminus of the Triassic basin the eastern boundary was not subject to intermittent and violent movements during the later stages of sedimentation, as it was in the south. Instead, the youngest part of the red-rock inlay consists, in some places, of unfractured boulder beds which were washed far out towards the center of the lowland; elsewhere, landslides brought masses of rock debris upon soft red and gray shales, which may have accumulated in shallow lakes; in still other localities, long stringers of red sediment reach far back into the eastern highlands. Many boulders in the conglomerate at the south end of Mount Toby are eight feet in diameter, and torrential mountain streams brought them to their resting place. A few are scratched and grooved, much like the boulders in the till left by the ice sheet; perhaps they signify the presence of snow fields and glaciers in the mountain range, but the scratches may have been acquired by avalanching. The landslide masses buried in the shales at the Sunderland caves show that the mountain front was steep, and the ancient talus or slide rock near the Central Vermont Railroad south of Roaring Brook shows plainly that the mountain front was a precipitous cliff of granite. The stringers of conglomerate extending eastward into the granite upland south of Montague, north of Leverett station, at Amherst, and again near Granby, are alluvial fill in ancient mountain gorges.

This old mountain mass stood out as a long, straight range extending from a point east of New Haven northward into New Hampshire. It was of moderate height in Connecticut, but it became higher and more rugged to the north; glaciers may have nestled around its crest east of Deerfield, and its front was an impressive slope of slide rock. Granite gorges with tapering gravel plains, dry one day and raging torrents the next, fingered eastward into the mountain block. At that time the Connecticut Valley was much like the land east of the Sierra Nevada in California, where greater contrasts in heights and depths are to be found than in any other part of the United States.

Like the valley east of the Sierras, the depression in central Massachusetts contained playa lakes and intermittent streams. Sand brought by the mountain torrents clogged the channels and spread into broad alluvial plains, while silt accumulated in muddy lake basins. Black sandy shales now mark the sites of the lake beds, and their black color comes from the coaly remnants of Triassic plants. Some swampy lake margins supported peat bogs, which have been preserved in coal seams two to three inches thick between Granby and South Hadley. Many of the lakes lasted long enough to become stocked with half a dozen species of fish. But the fish led a precarious existence, and their skeletons were buried in great numbers in the upper lacustrine layers when the lakes dried up, and dust and sand drifted over the parched basins at Durham, Connecticut, and at Sunderland, Massachusetts. The remains were interred even more effectively when cloudbursts in the hills brought thick layers of gravel out over the ancient lake beds.

Most of the lakes and ponds were ephemeral, but the fact that their presence was more than a mirage in a Triassic desert is clear from the ripple-marks retained on their sun-hardened surfaces, and from the impressions of objects which touched them while they were still soft. Stray series of parallel furrows record the passing of drifting shrubs, and the abrupt disappearance of rain-drop imprints at a well defined line in the hardened mud marks the exact position of the water level in a few of these Triassic water bodies. Footprints register the activities carried on by a bizarre animal population. Beside the road to the French King Bridge and in the river bed at Turners Falls the ripple-marked surfaces contain the impressions of many feet, and the dinosaur tracks at "the Riffles" beside the Northampton-Holyoke highway are known throughout the country. In Connecticut, Middletown and Durham are famed for their tracks, and the impressions left in the playa beds by muddy feet are so widely distributed throughout the lowland that it must have taken a lot of walking by many generations of dinosaurs to leave such an ample record.

Some of these three-toed animals were like the modern lizards and walked on all four feet; but the great majority walked on two feet and, like the kangaroos, used their tails to balance their bodies, and their short fore limbs to support them when they crouched. In any single playa deposit, variations in the sizes and kinds of footprints reveal that many individuals made them; yet strangely, most of the tracks at any one place are headed in a single direction. Apparently the herd instinct must have been strong in these reptiles, as it is in kangaroos or in a flock of turkeys, all following a leader, with only an occasional individual going off to one side or back-tracking in a display of independence. And so the dinosaurs dominated the life in the early Connecticut basin, as it sank and trembled, and as mountains rose to the east; on dry days and days of cloudburst, on hot days and days when frost crystals formed in the mud, they roamed the plain, as the lowland settled nearly two miles and filled to the brim with red sands, muds, and marginal gravels.

The ancient ash heap grows thicker east of the Connecticut River, and it is more than 3,000 feet from top to bottom around a series of massive blue-black rock-columns southeast of the Mount Holyoke Hotel. These are the lava-filled necks of craters which became quiescent with the dawn of the dinosaur days. The ash deposit, called the Granby tuff, grows thinner eastward away from the craters and disappears completely northeast of Granby, where a stream deploying from a valley in the eastern mountains washed it away as fast as it fell and left coarse gravel in the form of a huge fan.

The floor on which the ash came to rest was not everywhere the same. Where now it crosses the Northampton-Holyoke highway and the Amherst-South Hadley road it was a lava flow; but north of Granby and at numerous places between the Hockanum and Amherst-South Hadley roads the ash lies on conglomerate. Along the Amherst-Springfield power line, a block of the conglomerate floor was pushed up five hundred feet above the same beds farther west, forming a small block mountain which was entirely buried beneath the ash. Similar block mountains can be observed under the blanket of ash, especially on the south side of the Holyoke Range; and renewed movement subsequently affected many of the blocks north of Granby, where the ash deposit and even some of the sediments laid down in the earlier days of the dinosaurs were fractured and displaced. As a rule, along any one fault, the block on the east was pushed up and moved southward; and the block on the west was pressed down: as a group, the fractures may form the beginning of the great eastern border fault which bounds the basin farther south.

The volcanoes which made the Granby tuff or ash bed erupted intermittently for a long period of time. Usually, the river which emerged from the eastern mountain range brought so much fluvial debris that ash is not in evidence except in the immediate vicinity of the craters located between the Notch and the summit of Mount Holyoke. Even though alluvial sands and gravels supplant the tuff here and there, the river did not succeed in closing or quenching those fiery vents. The rocks now present recount a struggle in which, at times, the river encroached upon the cinder cones; at others, the ashes choked the stream and buried its alluvial wash.

While the volcanoes rumbled and erupted, earth forces intermittently thrust the eastern mountain range southward and upward, dragging the eastern margin of the lowland with it and upturning the sedimentary fill, much as a plow might upend a layer of snow at the roadside before shearing it off and pushing it out of the way. The relentless movement caused the entire eastern floor of the basin to be broken into blocks; the easterly ones were piled against the westerly, and their eastern edges were pushed down into the basin floor and the western borders rode up on their neighbors. Through all this tremendous disturbance the great stream pouring out of the mountain pass kept the elevated blocks cut down and the small basins filled in. Earthquakes, erupting volcanoes, and shifting rivers made life for the dinosaurs troubled and a bit uncertain.

Only once did the volcanoes dominate the situation in the valley, and that was very early in their history. A group of vents, localized along a southward trending zone about a mile west of the Notch, and another group along the present course of the Connecticut River from Turners Falls to Sunderland poured out billions of cubic feet of black basaltic lava into the center of the lowland. Eruptions followed in such rapid succession that the rivers never scoured the surface of the earlier flows. Lava piled up 400 feet thick in the center of the basin east of the Mount Tom Range; it moved eastward in a flow which thinned against the fans of rivers issuing from the eastern mountain, and it ended in a formidable wall of scoria confronting the mountain streams. Lava buried the northern basin from Sunderland to Turners Falls and beyond, while the southern basin filled from Northampton to New Haven. But lava dominance was short-lived, and even before its bubbly surface reddened to the weather, streams had covered it with gravel.

The lava flows are the most resistant materials used in the lowland design. They form the ridge east of Greenfield in the northern basin. The Holyoke and Mount Tom Ranges are remnants of these flows, tilted at moderate but varying angles by the recurrent movements which enlivened the epoch of dinosaurs and volcanoes.

The most spectacular episode of lava extrusion was localized in a small volcanic center situated about one mile west of the Notch in the Holyoke Range. All flows in the range moved away from this center, and before the great outpouring took place, minor explosive outbursts had built cones of ash with bases up to a mile in diameter. Small lava tongues are interspersed with the ash beds, and mixtures of sand and lava tell of breaks through the 1,500 feet of sandy fill which was rapidly accumulating in the basin. Throughout this early period of volcanic activity the streams brought out so much wash from the eastern mountains that they soon dominated the scene in Massachusetts, and in Connecticut volcanoes gained ascendancy for one brief moment of geologic time, when an early flow covered much of the valley from Hartford south.

The first and oldest ingredients in the central design are entirely red. The materials are fragments of older rocks--granite and gneiss, schist and pegmatite, feldspar and quartz. They are invariably coarse, for every layer of inwashed sediment has pieces over an eighth of an inch in diameter, and only the coarser particles were smoothed. The finer particles were not moved about enough to have their sharp corners worn away. The pebbles and clay in the thick layers of conglomerate at the French King Bridge were dropped by rushing, overloaded torrents deploying on a lowland--a situation not unlike the one at Townshend, Vermont, during the hurricane deluge. Only fine debris was transported across the fans to the far side of the basin. The western hills made small contributions of sediment; but their streams brought particles which never exceeded an inch in diameter, and in quantities so moderate that the fragments underwent some sorting and sizing as they were spread over the lowland. From the very start the valley was deeper near the east wall than the west; and the eastern mountain block was greatly elevated, whereas the western block was simply a hilly upland.

The edge of the eastern mountain mass is located at the French King Bridge and passes half a mile west of Montague. Its location beneath the younger fill is known less perfectly farther south, but it seems to extend through Amherst, certainly west of South Amherst and Granby and probably east of the Notch. At least two mountains rose above the ancient lowland floor; the northern one is a long ridge of schist between Bernardston and Mount Hermon, and the other is Mount Warner. Mount Warner is an island of highland rocks in a sea of red sandstone fill. The Bernardston ridge resembles a peninsula in somewhat analogous sedimentary surroundings. The two eminences reveal the form of the valley floor and the western hills at the dawn of the Triassic period, for they were spared from destruction by burial, until deep erosion exposed them again in Miocene time.

Hot springs the world over register their presence by leaving deposits of unusual minerals, and they have left this sort of record at Loudville. Here the coarse sandstones of the lowland rest upon gneiss, and at the south end of the Loudville lead vein barium sulphate crystals, called barite, formed in the sand before it was cemented into solid rock. The crystals are the product of highly charged mineral water, rising through the sands from a subjacent fissure. The fissure itself is also filled with barite, and with galena and quartz as well. It is the vein which was worked in the old Loudville lead mine. There are other veins in the western and eastern highlands at Hatfield, at the Northampton reservoir near Whately, and at Leverett. All are in fractures which were still partly open when the valley first took form.

The rocks which formed the high eastern mountain range of Triassic time and the rocks which made the old western hills and underlay the basin floor comprise essentially a single group characterized by its complexity. At one place the rock resembles sandstone, but the layers stand on end; at another, it looks like shale, but the stone breaks across the color banding instead of parallel to it; and at a third place a fissure seems to have opened and had a crystallizing melt poured into it. These tabular, filled fissures can be found nearly everywhere, coursing in every direction and at all conceivable inclinations to form a network that binds the older rocks into a firmly knit whole. The fillings, or dikes, are like reinforcing rods, holding the rocks together and withstanding the agents of destruction. Thus, the story of the highlands has three distinctive phases,--a relatively young phase when the interlacing reinforcements were poured into fractures; a somewhat more remote stage, when the bedded rocks were crumpled into their inclined positions; and an earlier stage, when the bedded rocks were deposited. The geologic dates of these three events may vary from one locality to another, and they certainly are different in the Eastern Upland as compared with the Western Upland; but the events always occurred in this sequence and constitute the broader aspects of the story at all places.

The Eastern Upland includes the land between the Connecticut Valley and the Atlantic Ocean. At present, it has the general form of a broad rolling highland with ridges and valleys that have a north-south trend. Close inspection shows that the rocks in the ridges are different from those in the long valleys. Also the layering of the materials ranges from a vertical attitude, as at Ware and Brimfield, to undulating and almost horizontal positions, as at Spencer and Worcester.

Through vertical and horizontal beds alike run those reinforcing sheets--some tabular and vertical, called dikes; others also tabular but horizontal, called sills; and some are just huge, irregular masses without visible bottoms, called stocks and batholiths. Some of them, composed of uniform, small, light-colored minerals, are granite; others are made entirely of large minerals over an inch across and are called pegmatite; a few, with cuneiform intergrowths of a dark mineral in a light one, arranged like Arabic writing, are known as graphic granite.

Every one of these masses flowed into the rocks along fractures and other zones of weakness, crystallizing as they lost their heat and solvents to the hot springs of that ancient time. They are all invaders, or intrusives, which inserted themselves into the older beds. Whether they were squeezed into the fissures by the pressures that crumpled the original beds into their upturned positions, or whether they, like the liquid in a hydraulic press, transferred pressure from a deep reservoir to the walls of the fissures and so pushed the beds into their distorted forms, is unknown. Two features are clear; the distortion of the beds and intrusion of the liquid bodies were almost simultaneous, and the hot springs associated with them were still active at the dawn of Triassic time. These profound disturbances transformed the land into a series of elevated, wave-like folds, and rains promptly began to tear away at the summits of the newly raised mountains. From them was carved a serrate and rugged landscape, part of which was later buried beneath the Triassic fill.

Among the strata of the Eastern Upland which were folded, intruded, baked hard, and stewed in hot spring water, one group stands pre-eminent. It forms a broad band starting north of Worcester and reaching to Providence and beyond. Nearly everywhere it carries coaly material or impressions of plants which are now extinct, but which flourished in the Coal Age or Carboniferous period. Some of the coal seams were mined in the Providence basin, but they had been so heated by intrusive granite that they are partly graphitic and proved difficult to burn. The great extent of some of the coal seams suggests a panorama of immense swamps, and of land so flat that, for long periods, streams brought no sediment, and the trees and water-loving plants furnished the only fill. At other times sluggish rivers, flowing from the northwest, laid thick layers of sandy mud over the surface of the bogs. The alternating muds and coal seams are thousands of feet thick, and they record the story of a basin which sank as fast as it filled--a depression which was never built high enough to be a well drained plain, yet never subsided sufficiently to be inundated by the sea. The Carboniferous peat bogs and mud flats may have extended westward almost to the Connecticut Valley; and farther to the northwest they were bounded by a chain of rolling hills.

The rock floor of the coal basin contains a variety of ancient materials. Some rocks were river deposits, some were marine limestones, a few were lava and volcanic ash, and many were granite and gneiss which crystallized at great depths and became exposed only after streams had stripped away the thick overburden. The basin floor thus holds a complex story, in which land and sea, vulcanism and quiet, erosion and deposition, all played their respective roles. Only in the west, along the margin of the Connecticut Valley, is the involved story at all clear. And in the Western Upland across the red-rock inlay, it is possible to see some of the land as it was before trees took root in the swamps, and rivers brought sands and muds from the vegetated hills that hemmed in the coal basin.

Many years ago, when transportation facilities were not what they are now, New England settlers mined iron ore from the hill north of Bernardston and smelted it in local charcoal furnaces. The rocks containing the iron are creased into sharp, close folds, and they came into such close contact with a hot granite intrusive that their minerals were changed by its action. This granite, however, is older than the one which is associated with the disturbed Carboniferous beds, for it was intruded when the Devonian sediments from Gasp? to Connecticut were deformed. It was this profound disturbance that turned the red rocks of Roche Perc? from a horizontal to a vertical position and raised a mountain range which stretched through all of northern New Brunswick, Maine, the lowland section of New Hampshire, and a belt extending for some miles east and west of the Connecticut Valley. The eroded remnants of these Shickshock Mountains formed the backdrop for the great Carboniferous coal swamps in Rhode Island, Massachusetts, and Acadia.

The iron ore was a hot spring replacement of a limestone containing shells of sea organisms which lived when chordate animals first became abundant. This was the Devonian period in geologic history--the time when a backbone appeared essential in every really high-grade animal. The limestone rests upon a beach gravel, now consolidated into a quartzite conglomerate. The gravel consisted of small white quartz pebbles which came from the many veins in the steeply inclined slates of the adjacent coast.

Marine deposits of Devonian age are found as far south as Leverett, and scattered outcrops indicate that the old seaway reached northward up the Connecticut, entering Canada east of Lake Memphremagog. Thence it spread eastward to Gasp? and westward to Montreal, and around the north and west side of the Adirondack Mountains into New York State. A low rolling land where the Green Mountains stand today formed the western shore of the Devonian sea for many miles northward into Quebec. The Adirondack and Taconic Mountains were a fused aggregate of undulating uplands which limited the seaway on the south along the International Boundary. Its eastern shore lay far beyond the horizon of the region described in this brief account.

The rocks of the old Devonian coast in Massachusetts were chiefly slates, cut by many quartz veins. They are exposed along the Mohawk Trail in the ascent from Greenfield to Shelburne Summit, and they continue northward in an almost unbroken band through Bernardston, Brattleboro, and Northfield to Lake Memphremagog. They contain casts of planktonic life which inhabited the Ordovician seas in these northern latitudes, and the Ordovician strata, together with still older Cambrian sediments found below them, meet the Devonian beach deposits at a sharp angle, just as the slates along the coast of Maine meet the modern beach sands and gravels. Like the slates of Maine, they were eroded deeply before the beach existed, and their slaty structure and their steeply inclined attitudes were acquired in a still more ancient epoch of deformation.

The folded rocks of Ordovician age flanked the highland area which now constitutes the axis of the Green Mountains. West of the Green Mountains they make the Taconic Range, and to the east they appear in ranges that go under a variety of names, including the Northfield and the Lowell Mountains. In the Taconics the folds have the shape of waves advancing westward from the center of disturbance in the Green Mountain axis; within the Connecticut basin the Ordovician folds have wave-fronts which advance from the same axis eastward across the Memphremagog sea. Along the eastern margin of the old land a series of dark green intrusives called peridotite welled up from the depths of the earth, and they now cut through the rocks extending from Chester, Massachusetts, to Thetford Mines, Quebec; they are like giant boundary posts marking the ancient line of demarcation between sea and land in Cambro-Ordovician time.

Originally the folded strata in the Taconic region were deposited in clear marine waters, where calcium carbonate accumulated rapidly. But the sediments of the same age east of the Green Mountain land represent an unbroken succession of hardened muds, which rest on sandy muds, and on fine and coarse products of violent volcanic eruptions--tuffs and agglomerates--and lava flows. No lime-secreting animals could thrive in this sea, although they numbered billions in the western waters; for only floating plankton could escape the interminable mud, and they drifted up and down the coast from Quebec to Connecticut. One or two straits may have connected the clear waters of the west with the muddy waters of the east, for some of the planktonic organisms have been found in the muddier sediments of the westerly waterbody.

The Cambro-Ordovician sea lapped even older rocks, contorted and cut by intrusives which bonded them precisely as much younger invading liquid rock bonded the younger sediments of the Eastern and Western Uplands. The older rocks were also laid in a sea--a sea so much more ancient than the Cambrian and Ordovician seaways that its shoreline and even its form and extent are at best conjectural. And when we study these oldest marine beds, we find that their ingredients were in part derived from still more ancient sedimentary rocks, which accumulated in the sea, and that these old beds were elevated into the land that supplied the waste now found in the oldest coherent section of rocks in western New England. Indeed, the dawn of the Cambrian period, when life first became abundant, was merely a half-way mark through geologic time. Although half a billion years have elapsed from the Cambrian to the present, another half a billion years reach still farther back towards the beginnings of earth history, beyond which science has not yet peered successfully. These billion years are but a finite segment of history, bounded by the infinite past and the infinity of the future.

It seems appropriate, therefore, to end our journey down the fourth dimension at this point, and as we retrace our steps, we can profitably survey the chronologic succession of events and scenes which followed each other from Cambrian time to the Twentieth Century A.D.

The Story of Central Massachusetts

The protracted story of central Massachusetts might be that of many another section of eastern North America, except for minor details. In Cambrian time an inland sea, well stocked with simple marine organisms, washed the shores of an archipelago which extended north and south through the Berkshire Hills, the Green Mountains, and the Notre Dame Mountains. Composed of rocks which themselves had had a long and involved geological past, the islands rose intermittently as streams and waves wore them away. Clear water and sandy beaches stretched along their western shore, and the original Adirondack Mountains were just visible from the summits of the higher islands. Swift streams raced down their eastern slopes, carrying gravels, sands, and silts into the eastern arm of the sea, and only free-swimming animals could survive in its turbid waters. For a time, volcanoes erupted and fumed along the entire eastern coast from Thetford Mines, Quebec, to Plainfield, Massachusetts, but their activity was short-lived. Only the streams which drained the broad islands endured, and they never ceased to pour mud into the eastern ocean. Gaps in the island chain permitted some of the free-swimming organisms to migrate to the western sea, where bottom-living plants and animals were actively secreting the limy shells and skeletons which helped build thick deposits of Cambrian limestone.

These conditions continued into the ensuing Ordovician period of geologic time, but gradually the situation changed. Again the volcanoes renewed their activity, and masses of dark peridotite were intruded along the eastern shore; the island chain rose rapidly, and the straits closed. The elevated land began to expand outward, and folds spread eastward on the east and westward on the west, like waves from a center of disturbance. So great was the pressure that portions of the old land were sheared outward over the folded sediments. The Taconic disturbance was on from the city of Quebec to the city of Washington; and the streams, like ants, kept at their endless task of carrying sand and gravel into any and every depression they could find. They piled up great thicknesses of Silurian sandstone in Maine and New York, and so effectively did they tear down the Taconic Mountains that the Silurian sea was ultimately able to penetrate the region from Thetford Mines, Quebec, almost to White River Junction on the Connecticut River.

One period later a Devonian sea followed in the wake of the Silurian sea, but its waters penetrated even farther south to Leverett, Massachusetts. The quartz gravels of its advancing beach covered the worn flanks of the Taconic folds. Sea animals left their shells to form a bed of limestone which may be seen today at Bernardston. But again the sea was shouldered aside by the restive land, which rose from Gasp? to Virginia. Much of the region affected by the Taconic disturbance was elevated again, and a broad band of Devonian sediments was folded closely through northern New Brunswick, southern Quebec, northern Maine, northern and central New Hampshire, and central Massachusetts. Granites welled up into the sediments, and dikes filled all the fissures. The baking, stewing, and reinforcing they gave to the older sediments made them so firm that they are still one of the most coherent and resistant series of rocks in New England and maritime Canada. This was the Shickshock or Acadian disturbance. Meanwhile the first forests took root on the long piedmont plains that spread from the rising mountains westward into the Catskill Plateau of New York State and eastward to the coast of Maine .

The margins of the piedmont plain sank. Vast, luxuriant swamps succeeded the old forests in Pennsylvania on the western piedmont, and in Rhode Island, Massachusetts, and Acadia on the eastern piedmont. The swamp vegetation later became the coal seams of eastern North America, and well does this time merit its name--the Carboniferous period. The Shickshock Mountains remained in the hinterland forming highlands from Spencer, Massachusetts, westward into New York State; but they were shorn of their crags, and only on rare occasions were the streams swift enough to carry silt into the swamps and to bury the accumulated peat.

Torn and twisted as New England had been by the two previous disturbances, it was to suffer yet again. The entire northern section of the eastern coal swamps began to rise, and the movement spread southward through New Jersey, eastern Pennsylvania, Maryland, Virginia, the Carolinas, and Georgia. Granites insinuated themselves once more into fissures in the elevated landmass; the rocks were pushed outward from the raised block; and the sediments of the coal fields were thrown into folds which diminished in magnitude towards Ohio on one side and Cape Breton Island on the other. This was the Appalachian Revolution. When it was over, even the youngest sediments were interlaced with granite sheets and dikes; they were cooked hard in hot spring waters; and they were crumpled into close, long north-south folds. The landscape was changed completely: mountains had replaced the peat swamps; and from their summits alpine glaciers were plucking rock fragments which they dumped into the Boston basin. Streams, too, cut deeply into the mountainous upland, but there were no other local basins in which the fluvial debris could come to rest.

This was, in brief, the course of events which transpired in that era of geologic time called the Paleozoic. Twice as long as all ensuing time, the era was one of kaleidoscopic change, with placid seas, eruptive volcanoes, swift streams, and towering mountains competing for the lead roles in three rather similar historical cycles. When the Paleozoic era was over, the matrix of tough, resistant rocks was ready for the delicate inlaid design which was imposed upon it in the Triassic period.

There was nothing tranquil about Triassic time. While hot springs, born in the cooling granites, still oozed from rents in the mountainsides, a tremendous 100-mile-long rift tore through the east margin of the old Shickshock Mountain foundation. The rift was a clean break at some places, but elsewhere it was splintered and offset. Each northern sector of the break invariably ended west of the beginning of a southern one, and the intervening rock is characterized by multiple fissures with more or less displacement of their walls.

The block east of the rift moved south and rose, while that to the west was depressed into a tilted and asymmetric basin. Mountain streams flowing eastward to the Atlantic were caught at the base of the rift, and a new set of torrents dashed down the west-facing scarp of the elevated block. After every cloudburst these new streams left their contributions of boulders in screes along the east side of the basin. The gravels steadily increased in thickness, covering the hills and valleys that furrowed the lowland floor. Much of the ancient relief still lies buried beneath the fill, but some of the eminences were exhumed one hundred and fifty million years later and have received man-given names like Mount Warner and Bernardston Ridge. As the basin subsided vertically for more than a mile, the mountain streams spread fans westward across most of its floor, restricting the contributions of the western rivers to a zone which is now less than two miles wide. The largest of the eastern rivers wore a valley three miles wide where it entered the lowland northeast of Granby.

Then volcanoes broke loose in the basin floor. Lava oozed through the sand west of the Notch in the Holyoke Range, and it frothed out of the openings or was blown violently from them. But by sheer persistence the rivers still dominated the scene as volcanic activity waxed and waned, and 1,500 feet of alluvial wash piled up around the volcanic cones. The energy of the volcanoes was ultimately spent, but for some time lava poured out of craters along a line extending southward from the main eruptive center, and from a second center which approximates the course of the Connecticut River from Sunderland to Turners Falls. It flowed westward into the middle of the basin in a series of sheets until it was 400 feet deep; it pressed upward against the sand plains along the western hills; it surged east up the fan slopes where it ended in a frothy wall; and it spread southward from these two centers and from others to New Haven. The lava, now tilted, gives substance to the Greenfield Ridge, the Mount Holyoke and Mount Tom Ranges, and the long line of hills that pass through Hartford and Meriden.

Spectacular was this outburst in its time, and profound was its influence upon later scenery, but short was its duration. Before weather could redden the lava surface, streams washed gravel over it; and only at the main centers between the Mount Holyoke Hotel and the Amherst-South Hadley road were the volcanoes able to hold out against the relentless activity of running water.

The block east of the rift continued to move southward and to rise, while the streams draining it entrenched themselves in an effort to remain at grade with the basin floor. The moving mountain mass pushed the lava flow up on end and twisted its eastern edge around, dragging it along to the south. The rock splinters which were formed in the process sliced the basin sediments into small blocks, some of which can be seen north of Turners Falls and also at the Holyoke Range. Ultimately the upward and southwestward movement along the rift piled the eastern blocks against the more westerly ones, pushing the west side of each eastern block up on the east side of the adjacent western one, and depressing its eastern side more deeply into the basin floor. The many fractures which were made weakened the basalt lava sheet along certain zones where, in recent time, the elements have worn the notches in the Holyoke Range.

Streams from the eastern highland stubbornly filled up the holes and planed off the raised blocks during the entire period of intermittent movement. In the midst of the tussle between earth forces and fluvial agents the volcanoes again broke into explosive eruptions, and volcanic ash filled many of the block-like depressions all the way from Granby to localities south of Holyoke. Then the fiery vents cooled, and the earth movements diminished in their vigor. But they left a mountain front so steep that talus and landslide deposits accumulated at its base near Mount Toby; and the block mountain range was so high that glaciers may have wreathed its summit. The mountain mass descended southward, and it was penetrated by at least one low pass northeast of Granby.

In the basin itself, alluvial fans encroached from the eastern mountain front, but out in the middle of the valley ephemeral playas and shifting lakes were numerous. Rushes fringed the lake shores; fish stocked their waters; and dinosaurs lumbered over the adjacent flats. The region was one of violent rains and seasonal droughts, of hot days and frosty nights--a semi-desert country lying in the lee of the Appalachian ranges, somewhat as the intermontane valleys of the West lie in the rain shadow of bordering mountains. Eight thousand feet of sediments poured into the Triassic trough while these conditions lasted, but the situation altered slowly as the Jurassic period dawned.

Throughout earth history, vulcanism and mountain-making have been spasmodic events; but so long as rain has fallen and water has run downhill to the sea, the unspectacular rivers have never relinquished their task of reducing the lands to the lowest grade on which water will flow. During all of the Jurassic and Cretaceous periods, and even into the Eocene epoch of the Tertiary, New England's rivers worked towards this end, and they came as close to attaining their goal as the restless earth has ever permitted them to do. The region from the Atlantic to the bases of the Green Mountains and the White Mountains was reduced to a broad, faintly terraced erosional plain. Not all of it was leveled, for Mount Wachusett, Mount Monadnock, the summits of Mount Greylock and Mount Ascutney resisted the wear and tear of the weather and of running water, and retained some of their original stature. At the headwaters of the streams the Green Mountain chain and the White Mountains also withstood reduction to the common level, forming the divide between St. Lawrence and Atlantic drainage. Such rivers as the Merrimack, the West, the Deerfield, and the Farmington followed somewhat different courses than they do today, for some of the drainage heading in the Western Upland of New England flowed straight across the red-rock valley to the sea.

During Tertiary time the entire region rose vertically as a unit. The rise was intermittent, punctuated by long stillstands of the upland with respect to the sea. One of the earlier uplifts carried the land some 200 feet higher; and although the rivers maintained their courses, they deepened their valleys and ultimately widened them into broad, open plains far back towards their headwater reaches. In the resistant rocks on either side of the red-rock basin the valleys were sharp and well defined, but in the soft Triassic sediments the rivers cut wide swaths, nearly eliminating the low divides which kept them in their independent courses.

In Middle Tertiary time renewed uplifts occurred, and ultimately the strathed surface was elevated 1,800 feet inland at the Green Mountain divide. Once more the rivers started busily cutting down; but in a protracted stillstand, while the New England upland still lacked 700 feet of its present elevation, the Atlantic Ocean planed off the hills in southern Connecticut as far north as Middletown, and the Farmington River adopted a more direct route across the marine plain to the sea. Before the West, Deerfield, and Westfield Rivers could lower their channels to grade in the reinforced rocks of the Eastern Upland, a tributary of the Farmington worked headward along the poorly consolidated red rocks of the basin and diverted the waters of the northern streams into its own channel. This was the birth of the Connecticut River, and in late Tertiary time, the energies of the new-born stream were effectively expended widening the whole of the Triassic basin. Even some of its larger tributaries developed wide valley floors with steep walls in the hard crystalline rocks of the uplands. Only the lava flows and the buried old-rock mountains withstood planation in the red-rock basin. The flows form such trap ridges as Greenfield Ridge, the Mount Holyoke Range, the Mount Tom Range, the Hanging Hills of Meriden. Exhumed mountains are typified by Mount Warner.

All of northeastern North America was raised to great heights in late Pliocene time, and the Atlantic Ocean withdrew at least fifty miles southeastward from the present shoreline. The rejuvenated rivers deepened their valleys, forming narrow, sharply incised canyons like the gorges of the Hudson and the Saguenay; and the Connecticut made a deep groove in the lowland floor, cutting to depths which have been partly disclosed by drilling at the Calvin Coolidge Memorial Bridge and the Sunderland Bridge.

While the land stood in this high position, one winter's snow in the White Mountains failed to melt before the next began to fall. Snowfall accumulated upon snowfall, covering not only the White Mountains, but all of Canada and New England; and the Ice Age was here to stay more or less continuously for a million years. The ice piled up against the highest mountains and ultimately rose so far above them that it slid over their tops without attempting to detour around them. Its surface may have been 13,000 feet above sea level in northern New Hampshire, and its surface slope, which is estimated at 150 feet per mile, would give a thickness of 10,000 feet at Northampton. The continent yielded slowly under this great load, and it sank until all of the elevation gained in the Pliocene movement was wiped out, and more besides. The ice radiated from the centers of maximum accumulation--at first from the White Mountains, and then from northern Ontario, and finally from Labrador. The continental glacier crept southward to Long Island and Martha's Vineyard, where its front melted in the waters of the Atlantic as fast as new ice came up behind. It dragged and pushed and carried debris, only to dump it in a hummocky ridge, like a rampart, to mark its farthest advance.

At last the glaciers started to melt even faster than new masses moved down from the north, and the ice front began to recede 400 to 700 feet per year. The sea followed it, up the Hudson, up the St. Lawrence, in over the coastal lowlands for a short distance; and everywhere pounding waves made beaches at the water line. And in the path of its slow, deliberate retreat, the glacier left rock debris--boulders on the hills and in the valleys, boulders everywhere; all the landscape was marred and desolate.

The ice had weighed the pre-glacial valleys down more deeply in the north than in the south. One such valley was the Connecticut Lowland, in which water gathered to overflow-height at Middletown. Thus Lake Springfield came into being, and it spread northward as the ice front receded. North of the Holyoke Range another lake formed, and this northern body of water has been named Lake Hadley. Streams flowed off the ice, off the hills--flowed with unimpeded vigor, for there were no trees or grass to retard the run-off. Deltas grew out from the shores, and annual layers of clay settled on the lake bed.

The ice grew thinner, its area smaller, and its load lighter; and as Mother Earth lost her heavy burden, the land rose, more in the north than in the south. The differential rise decanted the water southward out of the lake basins, and the seas retired from the coastal lowlands. Old shores and sea beaches remained as flat terraces sloping gently southward. The rivers raced down the steep beach slopes to the old lake floors and sea bottom. They cut their channels deeply into the unconsolidated deltas and meandered back and forth over the flat, ungraded lacustrine plains, as if uncertain where to flow. They flooded the lands in the spring, leaving loose sand and silt for the winds to blow when the water was low. Sand dunes rose near the river banks at North Hadley, Sunderland, Hatfield, and South Deerfield; but the march of the dunes was arrested as post-glacial vegetation repossessed the land. It was at this point in the story that man found and settled the Connecticut Valley, becoming a witness to the geologic work of the river and an aid to the work of the wind as his plow bared the fertile soil to the elements.

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