THE CAMBRIAN PERIOD 69 



climate was not essentially different from that of comparatively 

 recent geologic time, but that climatic conditions were much more 

 uniform over the earth than now. 



Economic Products 



Cambrian rocks, such as the Potsdam sandstone and Little 

 Falls dolomite in New York, furnish considerable quantities of 

 building stone for local use. 



Roofing and other slates of Cambrian age are extensively quar- 

 ried in Vermont and eastern New York. Also the famous slate 

 quarries of Wales are in rocks of this age. 



No very important metalliferous deposits are known in Cam- 

 brian rocks. 



Life of the Cambrian 



Stage of Evolution of Cambrian Life. — The life of the Cam- 

 brian possesses a particular importance because, excepting the 

 few scant organic remains found in upper Algonkian rocks, the 

 rocks of this age contain the oldest known assemblage of distinct 

 fossils. Many hundreds of Cambrian species have been described. 

 Even here, however, the organic record is very incomplete both 

 because many Cambrian fossils have not yet been discovered and 

 because a vast number of Cambrian organisms must never have 

 been preserved as fossils. Although Cambrian fossils are scant as 

 compared with those of other Paleozoic systems, nevertheless a 

 striking fact is the large number and complexity of organisms 

 represented. All of the sub-kingdoms of invertebrate animals 

 are represented, though nearly always by only the simpler types 

 of each sub-kingdom, and this together with the positive evidences 

 for pre-Cambrian life, make it perfectly evident that organisms 

 existed and developed (evolved) for a vast length of time before 

 the opening of the Cambrian. It is generally agreed that fully 

 half of the evolution of organisms had taken place before the 

 beginning of the Cambrian period. 



In spite of so much pre-Cambrian evolution of organisms, it is 

 to be remembered that, as a result of post-Cambrian evolution, 

 literally enormous advancement has been made, so that Cambrian 

 forms are really simple or primitive as compared with many of the 

 highest living forms. To illustrate, there is a vast gulf between 

 the degree of organization of the highest Mammals of today and 



