88 



The Ottawa Naturalist. 



[Nov. 



why the extinct trilobite should have needed a deep water 

 habitat. In fact, specimens in our collections show this form to 

 be present upon the surface of interformational conglomerate 

 layers — those curious bands which owe their origin to the edge- 

 wise packing and cementing of broken bits of sun-dried crust 

 upon a tidal flat — a characteristically shallow water phenomenon 

 exhibited by limestone strata scores and hundreds of feet in 

 thickness throughout large areas of the Cambrian in Wyoming, 

 British Columbia, Alberta, and Yukon. It may be of interest 

 to record here also the fact that brachiopods and trilobites have 

 been discovered in a massive Cambrian limestone composed al- 

 most entirely of Cryptozoon-like algal masses approximating a 

 foot in diameter and six to eight feet in length. The gradually 

 accumulating weight of evidence is thus strongly in favour of 

 the conclusion that neither marine faunas nor limestones are, 

 either of themselves or jointly, a criterion of deep water deposi- 

 tion, and that for much of the Cambrian the postulation of deep 

 sea basins is unnecessary. Moreover, we have shown this to be 

 true for at least part of a horizon whose faunas preserve their 

 individuality through the one thousand or more miles separating 

 the Nevada localities from those in British Columbia and Al- 

 berta, (d) 



Evidence of shallow water conditions in the Cambrian is 

 most striking, however, nearly 3,000 feet above the Stephen 

 formation at the line separating the Middle from the Upper 

 Cambrian. The base of the Bosworth formation (e) in the 

 Canadian Pacific Railway section and the base of the Lynx 

 formation (/) in the Grand Trunk Pacific section comprise 

 several hundred feet of red and yellow shales which are covered 

 with mud-cracks, ripple-marks, and casts of salt crystals two 

 inches or more in diameter. The emergence of the sea bottom 

 indicated by these occurences must have been prolonged, but 

 the quiet limestone forming conditions which immediately pre- 

 ceded thein soon followed. The occurence is -of special interest, 

 because the correctness of the division of geologic time into 

 major units is believed to be confirmed when those units are 

 discovered to represent periods of deposition separated by emer- 

 gences of the sea bottom. 



(d) Geol. Survey Canada, Museum Bull. No. 2, 1914, p. 113. 



(e) Walcott, Smithsonian Misc. Coll., vol. 53, No. 5, 1908, pp. 205-208. 

 (/) Idem, vol. 57, No. 12, 1913, p. 337. 



