CHAMBERS'S INFORMATION FOR THE PEOPLE. 



contents. As already said, geologists have divided 

 all the rocks into different classes, according to 

 their relative position and the fossils they contain. 

 The whole of the stratified rocks are divided into 

 eleven great systems, and each of these into sep- 

 arate groups, to which names have been given, 

 more or less descriptive of the strata to which they 

 are applied. The systems have been named chiefly 

 from localities in which they are largely or typi- 

 cally developed, as the Laurentian ; in some cases 



from important rocks they contain, as the Carbon- 

 iferous ; in others from their position or order, as 

 the Recent. They are given tabularly below, with 

 the reasons for the names, and their chief rocks, to 

 give a definite idea and to assist the memory. This 

 list should be carefully studied and comprehended 

 before going farther. These systems are also 

 grouped into three great Periods, and into two 

 great Cycles, according to the character and 

 advance of the organic life they contain. 



ROCK-SYSTEMS. 



These systems we shall describe in order, be- 

 ginning with the earliest, down to the most recent, 

 giving the appearance and composition of the 

 rocks, the uses to which they are applied, and the 

 fossils they contain. We shall also endeavour to 

 realise the state of the earth at each successive 

 epoch, the scenery then exhibited, and the plants 

 and animals that then enlivened the landscape. 

 Below the Lau~entian, another system is some- 

 times given as existing, called the Metamorphic 

 or Primary or Non-fossiliferous. It seems neces- 

 sary to abandon this system. As shewn (p. 22), 

 metamorphic rocks occur in all systems. The 

 assertion of the absence of fossils is premature, 

 and has always proved so in regard to other rocks, 

 and is unscientific. The term primary is objec- 

 tionable on like grounds. All existing rocks, as 

 far as yet known, seem to be comprehended under 

 the eleven systems given above, which we now 

 proceed to describe. 



I. LAURENTIAN SYSTEM. 



Description. Immediately above the Non-fos- 

 siliferous Metamorphic rocks lie the lowest of 

 those that contain fossils. These have received 



1 From Greek ptilaios, ancient, and zgon, an animaL 



* From Greek mesos, middle, and zSon, an animal. 

 3 From Greek cainas, recent, and zoon, an animal. 



* From Greek neos, new, and zdon, an animaL 

 34 



the name of the Laurentian System, from their 

 great development on the shores of the St Law- 

 rence, in Canada. It was only quite lately, in the 

 year 1863, that these rocks were grouped into a 

 distinct system, from the discovery in them of 

 certain fossil remains in Canada, having previously 

 been reckoned metamorphic. The Laurentian 

 System consists of certain schists, quartzose rocks, 

 and limestones, all very highly crystallised shew- 

 ing good examples of metamorphic rocks. They 

 form two groups, upper and lower. They contain 

 no sandstones or shales, that occur so frequently 

 in higher formations, such of these as once existed 

 having been changed by heat. The limestones are 

 very highly crystallised and metamorphosed, and 

 of great thickness. The rocks, however, are all 

 truly sedimentary, deposited under water, and 

 have received their present aspect mainly through 

 the agency of heat. They are found in Canada, 

 Ireland, Norway, and Sweden, and, perhaps, in 

 the north-west of Scotland. 



Organic Remains. The discovery of the fossil 

 remains that caused these rocks to be formed into 

 a separate system, was made in Canada, and 

 excited interest amongst geologists, because be- 

 longing to a period when organic existence was 

 thought impossible. The organism discovered 

 received the name of the Canadian Eozoon 1 or 



1 From Greek ids, dawn, and zdort, an animal. 



