CAMBRIAN SYSTEM. 27 



25. These formations closely resemble the preceding, and it is 

 often difficult to distinguish them, but they do not appear to hav>> 

 begun to form until the first had been disturbed by some great 

 geological convulsion ; for the strata of which they are composed 

 are not parallel to those of the rocks on which they rest, and they 

 differ from them by having fossils entombed in their substance. 

 They appear to have been formed by a slow and continuous 

 deposit of sand, mud, and other materials suspended in water, 

 and they consist chiefly of schists and calcareous rocks. The sea 

 seems then to have covered the greatest part of the known surface 

 of the globe, for we scarcely find a trace of terrestrial plants, and 

 immense depots of these strata, almost identical in character, are 

 met with in the most distant parts of the earth, as in Germany, 

 England, and America. 



26. To judge by the fossils concealed in these formations, the 

 globe was then inhabited by a small number of plants, belonging, 

 for the most part, to the family of fucus, and by a multitude of 

 marine animals, the forms of which differed widely from those now 

 existing. It is also remarked that most of these animals belonged 

 to the inferior classes of the animal kingdom, and, until lately, it 

 was believed no vertebrate animal then existed ; but within a short 

 time it has been ascertained there were marine fishes, for remains 

 of them have been discovered in certain rocks whose formation 

 dates back to this remote epoch. (Fig- 20.) 



27. The most ancient beds of the transition formation contain 

 very few fossils, wnile other rocks of the same formation are rich 

 in these remains ; these differences, which correspond with other 

 peculiarities of stratification, have led geologists to divide this period 

 into three divisions, called the CAMBRIAN, SILURIAN, and DEVONIAN 

 Systems of rocks. 



28. The CAMBRIAN (from Cambria, in Wales) or SCHISTOSE SYS- 

 TEM. The Cambrian rocks are the lowest sedimentary deposits 

 known. They are composed essentially of schistose grauwackes, 

 which pass through all shades of solidity, lustre and colour ; on 

 one side they unite with the mica-schists and gneiss, and on the 

 other with the coarse grauwackes, with which they are found inter- 

 calated. These rocks contain slate rocks, conglomerates, dark 

 limestone, and fine-grained slates of various shades of purple, blue 

 and green. In the Cambrian rocks the organic remains consist of 

 a few fossil brachiopods, polypa'ria, or coral animals, &c. 



25. How does the palao'ozoic formation differ from the primitive rocks ? 

 In what manner were the palao'ozoic formations produced ? 



26. At the period of the palae'ozoic formation, what description of organ, 

 ized beings lived on the earth ? 



27. How is the transition or palse'ozoic formation divided ? 



28. How is the Cambrian System of rocks characterized ? From what 

 is :*s name derived ? What is the geological position of the Cambrian 

 System ? 



