Fig. 648.—Conformable Strata.
Fig. 649.—Unconformable Strata.
Hitherto, no distinctly recognisable fossil has been discovered, with the important exception of the Eozoön Canadense, which has been pronounced to have been a gigantic foraminifer, growing layer upon layer, and thus forming reefs of limestone; the subject, however, is still a matter of dispute. The eozoön was discovered by Mr. J. M’Mullen in 1858 in Canada.
Fig. 650.—Nereites Cambrensis.
Granite was at one time considered to be the true primitive rock. Gneiss is a word of Saxon origin, and consists of the same materials as granite in different proportions. Mica-schist is made up of two of the same constituents as the granite and gneiss. They are without fossil traces.
The Cambrian system of aqueous origin may be said to contain evidence of the dawn of organic life. It is part of the clay-slate system, and the term “Cambrian” is taken from the ancient name of Wales, where slate is plentiful. Mica-slate is also very important. These Cambrian rocks are of the next oldest formation to the Laurentian, and all the various deposits may be examined in Wales, where also traces of volcanic and ice action may readily be perceived. In the pass of Llanberis one immense ice-borne block is very prominent; no agency but ice could have put it there as it rests. It is estimated that the Cambrian and “Lower” Silurian rocks are from 20,000 to 30,000 feet in thickness, and must embrace a very lengthened period. The fossils of these formations show that zoophytes and certain primitive crustacea lived in the remote ages when these rocks were formed by sedimentary deposition. We have scarce a trace of plant-life. The organic remains include annular worms, the first arrangement of the articulated animals according to Cuvier. The flora and fauna are, of course, very low in the scale of creation, when land and sea were so differently arranged.
