Page:A Treatise on Geology, volume 1.djvu/187

Cryptogamia vasculosa —	Equisetaceæ	above	90	species
	Filices	above	100
	Lycopodiaceæ	about	60
Phanerogamia	monocotyledoneæ		10
	Coniferæ		10
	Cacteaceæ		50
	Indeterminate		50
			——
			300	species

Fig.	1. Stem of a sigillaria always denuded of leaves.
	2. Stem of a large catamites.
	3. Stem and leaves of asterophyllites.
	4. Branch and leaves of lepidodendron.

Of the accumulated remains of these plants coal seams are really composed, and one cause of the differences amongst them is the different structural composition of the original plants. How far the above fossil flora is to be taken as exhibiting the true proportions of the tribes of plants living on the globe, at the time of the production of the rocks of the carboniferous system, is uncertain: since, when plants are swept down from the land into the sea, it depends on many unknown conditions what sorts of them shall escape the floods, or perish by maceration in the waters.

As a general rule, it may be said that the plants are confined to arenaceous and argillaceous deposits: they