Page:A Treatise on Geology, volume 1.djvu/147

 CHAP. VI. the true lower Silurian base. In all this thickness only a few organic remains occur either in Wales or Cumberland, and all the very lowest beds in Wales appear devoid of them. Perhaps this deficiency of the remains of life is the main character by which this "Lower Cambrian" system is distinguished from the strata above.

Organic Remains.—By whatever name these ancient strata shall in future be called, they must always bear to the philosophic student of geology a peculiar and paramount interest, as the oldest rocks in which organic remains are certainly known to occur. It may surprise the speculators in Cosmogony to hear that these, the most ancient forms of life known to us, are not plants, but animals: not even the lowest grades of their respective classes, but perfectly developed zoophyta, echinodermata, brachiopoda, and trilobites. No gasteropods or cephalopods are indeed as yet mentioned in these rocks, but we must be careful not to attach to this merely negative evidence more value than really belongs to it. Whether at the time of the formation of these ancient rocks in the sea, plants were growing on the land (whether, indeed, there were any neighbouring dry land), we must only conjecture: that plants might be growing in the sea, which nourished the shells and trilobites and zoophyta, may be a probable but not a certain inference; since sea-weeds do not alone constitute the food of conchifera or zoophyta. We found no satisfactory trace of plants in the fossiliferous rocks of Snowdon, nor are they common in Cumberland.

We cannot, from the few scattered species of fossils (yet very imperfectly known) which have been obtained from these ancient rocks, learn the conditions under which they lived; but they are of great value as the oldest monuments yet discovered of the creation of living things. The very rarity of their occurrence and the paucity of species confirm the general views advanced as to the cause of the absence of organic fossils from the still older systems of gneiss and mica schist; for these few remains, scattered through as many miles of stratified