36 GEOLOGICAL HISTORY. [CH, 



Director of the Canadian Geological Survey applied the term 

 Laurentian. These Laurentian rocks, with similar strata in 

 Scandinavia, the north-west Highlands of Scotland, in certain 

 parts of such mountain ranges as the Alps, Pyrenees, Carpa- 

 thians, Himalayas, Andes, Atlas, &c., have been classed 

 together as members of the oldest geological period, and are 

 usually referred to under the name of Archaean, or less 

 frequently Azoic rocks. In some of the uppermost Archaean 

 rocks there have been recently discovered a few undoubted 

 traces of fossil animals, but with this exception no fossils are 

 known throughout the great mass of Archaean strata. It is 

 true that some authorities regard the beds of graphite and 

 other rocks as a proof of the abundance of plant life, but this 

 supposition is not supported by any convincing evidence. 



The term Azoic ^ applied by some writers to these oldest 

 rocks suggests the absence of life during the period in which 

 they were formed. Life there must have been, though we are- 

 unable to discover its records. The period of time represented 

 by the Archaean or Pre-Cambrian rocks must be enormous^ 

 and it was in that earliest era that the first links in the chain 

 of life were forged. 



II. Cambrian. 



The term Cambrian was adopted by Sedgwick for a series- 

 of sedimentary rocks in North Wales {Cambria). In that 

 district, in South Wales, the Longmynd Hills, the Malverns^ 

 in Scotland, and other regions there occur more or less highly 

 folded and contorted beds of pebbly conglomerate, sandstones^ 

 shales and slates resting on the uneven surface of an Archaean 

 foundation. 



It is in these Cambrian rocks that trustworthy records of 

 organic life are first met with. Among the most constant 

 and characteristic fossils of this period are the extinct and 

 aberrant members of the Crustacea, the trilobites ; these with 

 some brachiopods, sponges, and other fossils comprise the 



1 Whitney and Wadsworth (84). 



