370 THE CAMBRIAN. [bull. 81. 



SUBDIVISION OF THE CAMBRIAN. 



In his admirable report upon the Devonian of North America Prof. 

 H. S. Williams expresses this opinion : 



The subdivision of any great geological system must depend in great measure 

 upon the differences in the faunas or floras contained, and, as I believe, 'this depends 

 in no small degree upon the geological changes which modified and shifted the geo- 

 graphical conditions under which the animals lived. A sandstone will not contain 

 the same species as a following limestone, and even in arenaceous shales a slight 

 change in the fineness or coarseness or in the amount of argillaceous mud mixed 

 with the sand modifies the composition of the fauna contained in it. 1 



There are not at present sufficient available data from the Cambrian 

 upon which to base comparisons with the same degree of refinement as 

 those made by Prof. Williams. It has been discovered, however, that 

 the predominant types of life of the Cambrian group are to be found in 

 shales, limestones, and sandstones. For instance, the genus Olenellus, 

 characteristic of the Lower Cambrian, is fouud in the shales, limestones, 

 slates, and sandy shales of the typical section in Northern Vermont. 

 I have found in the quartzites and in the pure limestones of the Pots- 

 dam epoch of the Adirondack subprovince the same species of Dikel- 

 ocephalus, Hyolithes, and Lingulepis. In the dark argillaceous shales 

 of the Middle Cambrian terrane of Newfoundland I found the same 

 species of Paradoxides that occurs in the iuterbedded limestones of 

 the same series a few miles distant. That Prof. Williams is correct in 

 relation to the great mass of organisms that existed during Paleozoic 

 time there can be very little if any question. As an example the corals 

 of the limestones of the north shore of the Strait of Belle Isle, on 

 the Labrador coast, are unknown, except in an almost identical lime- 

 stone at Silver Peak, Nevada, in the Rocky Mountain Province. It is 

 in the clearer limestones that the great bulk of the brachiopods, 

 pteropods, and other forms of life are found in the Cambrian ; but it is 

 a fact, nevertheless, that the predominant types of the Trilobita, char- 

 acterizing its three divisions, flourished upon and were imbedded in 

 sediments of widely different character. It is owing to this that they 

 become of so much importance as criteria in the correlation of the three 

 primary divisions of the group. 



In the Atlantic Coast Province the fauna of the Lower Cambrian, or 

 Olonellus zone, occurs in arenaceous limestones, pure limestones, and 

 shales. All of these are of a different character from those of the black 

 shales 200 feet above, in which the Paradoxides or Middle Cambrian 

 fauna occurs. The Upper Cambrian fauna is found in dark shales and 

 sandstones several hundred feet, if not a thousand feet, above the Para- 

 doxides zone. The three primary subdivisions of the Cambrian are 

 strongly defined by the sedimentation and faunas. In the St. Lawrence 



1 International Congress of Geologists, American Committee. Report of the subcommittee to the 

 session of the Congress held in London, September 17, 1888. Philadelphia, 1888. Report of the sub- 

 committee on the Upper Paleozoic (Devonic), H. S. Williams, Reporter, p. C 20. 





