With the Devonian things changed. The bad state of preservation of fossil vegetables belonging to this formation has not permitted us to study them perfectly; but, from the aspect of those which we possess, we conclude that at this epoch the vegetable kingdom was already vigorous and varied, and that nature while in its infancy put forth the carboniferous flora, the almost inconceivable exuberance of
Fig. 4.—Primordial Terrestrial Plants observed by M. Lesquereux in the Upper Silurian of America: 1. Psilophyton cornutum (Lesquereux). 2-4. Sphenophyllum primosis. 5. Annularia Romingeri. 6. Protostigma sigillarioides.
which has never since been equaled. This flora, to the description of which numerous works have been devoted, is still more interesting and important as furnishing the elements of the coal—the soul of industry, as it has so justly been called. We know that the conditions in which the coal-beds were formed very much resembled those in the midst of which the peat is now actually being formed. As Saporta has observed, in the Carboniferous epoch there were emersions upon a grand scale, emersions succeeding each other, flowing over and receding from the insular or continental space, until its recovery from the waters. This action of the waters would produce a low bank or shore around the primitive land, the relief of which would tend to become more accented, and at length would retain the waters coming from the interior and unite them at the bottom of extensive depressions. In this way were formed vast lakes, with vague banks and shallow waters, easily invaded by plants loving an aquatic station. If we join to this the humid warmth, the thickness of the atmosphere, charged with vapors, causing frequent and violent rains, we perceive how favorable were the conditions for the development of the carboniferous vegetation.
The plants of this flora belong exclusively to the two classes of vascular cryptogams and gymnospermous phanerogams. At the head of the cryptogams were the Calamarias, which recall on a gigantic scale the Equisetaceæ of our day; by their side Asteraceæ, Annularia, Sphenophyles; then come ferns of very varied form and structure, and Lycopodiaceæ of the type Lepidendroideæ. Certain plants, the Bornia, Calamodendreæ, and Sigillaria, form connecting links between cryptogams and phanerogams. These were gymnosperms, that is, plants assimilable by the class Cycadeæ to the conifers and the ac-
