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on the shale in contact with it. The reticulations are generally irregular, but sometimes they very closely resemble the veins of a reticulately veined leaf. One of the most curious specimens in my possession was collected by Mr. Elder in the Lower Carboniferous of Horton Bluff. The little veins which form the projecting network are in this case white calcite; but at the surface their projecting edges are blackened with a carbonaceous film.
"Journal of the Geological Society," June, 1871.
I have referred to these facts here because they are relatively more important in that older period, which may be named the age of Algae, and because their settlement now will enable us to dispense with discussions of this kind further on. The able memoirs of Nathorst and Williamson should be studied by those who desire further information.
Appendix, p. 676, edition of 1878.
But it may be asked, "Are there no real examples of fossil Algae?" I believe there are many such, but the difficulty is to distinguish them. Confining ourselves to the older rocks, the following may be noted:
"Fossile Flora," 1852, p. 92, Table xli.
Brongniart, "Vegeteaux Fossiles," Plate vi., Figs. 7 to 12.
"In garments green, indistinct in the twilight, They stand like Druids of old, with voices sad and prophetic."
Prophetic they truly were, as we shall find, of the more varied forests of succeeding times, and they may also help us to realise the aspect of that still older vegetation, which is fossilised in the Laurentian graphite; though it is not impossible that this last may have been of higher and more varied types, and that the Cambrian and Silurian may have been times of depression in the vegetable world, as they certainly were in the submergence of much of the land.
These primeval woods served at least to clothe the nakedness of the new-born land, and they may have sheltered and nourished forms of land-life still unknown to us, as we find as yet only a few insects and scorpions in the Silurian. They possibly also served to abstract from the atmosphere some portion of its superabundant carbonic acid harmful to animal life, and they stored up supplies of graphite, of petroleum, and of illuminating gas, useful to man at the present day. We may write of them and draw their forms with, the carbon which they themselves supplied.
Examination of Prototaxites , by Prof. Penhallow, of McGill University.
Prof. Penhallow, having kindly consented to re-examine my specimens, has furnished me with elaborate notes of his facts and conclusions, of which the following is a summary, but which it is hoped will be published in full:
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