1915] The Ottawa Naturalist. 87 



SHALLOW WATER DEPOSITION IN THE CAMBRIAN 

 OF THE CANADIAN CORDILLERA.* 



By Lancaster D. Burling. 



During the field season of 1915, the writer was engaged in a 

 strati graphic study of the Cambrian rocks along the Canadian 

 Pacific and Grand Trunk Pacific railways in British Columbia 

 and Alberta. One of the most striking features observed was 

 the very considerable evidence of shallow water conditions of de- 

 position in the limestones of the region. 



The Stephen formation ( i) occupies a central position in the 

 Middle Cambrian and forms a two or three hundred foot shelf be- 

 tween clift^s of massive limestone each a thousand feet or more in 

 thickness. In the vicinity pf Motmts Stephen and Field, on the 

 Canadian Pacific Railway, it includes those striking Middle Cam- 

 brian faunal horizons to which the terms Ogygopsis shale and 

 Burgess shale have been applied. Here the limestones and shales 

 of which it is composed betray no evidence of shallow water con- 

 ditions of deposition; in fact it is hard to see how the jelly fish, 

 sea cucumber, sponge, worm, crab, and pteropod fauna of the 

 Burgess shale (b) could have been preserved in strata deposited 

 outside of the most sheltered of habitats. In Castle Mountain, 

 30 miles southeast of the locality to which these faunas appear 

 to be confined, however, the limestones of the Stephen forma- 

 tion, which are both coarse and fine grained and apparently pure- 

 ly calcareous, are very largely mud-cracked and ripple-marked. 

 The areas outlined by these mud-cracks vary from one inch to 

 three or four feet in diameter, and the distance between crests 

 of the ripple-marks varies from one inch to two or more feet, some 

 of the larger ripple-marks being impressed upon layers carrying 

 limestone conglomerate pebbles two inches or more in diameter. 

 Nearly all of these limestones carry an abundant trilobite and 

 brachiopod fauna. Pure limestones carrying what we have been 

 accustomed to regard as marine faunas thus bear unimpeach- 

 able evidence that they have not only been deposited under 

 shallow water conditions, but that in many cases they have 

 suffered prolonged exposure to the air. Glottidia, Kraussina, 

 Terebralulina, Lingula and Discina, among recent brachiopods, 

 are known {c) to live at or above low tide, and there is no reason 



* Published with the permission of the Deputy Minister nf Mines. 



{a) Walcott, 1908, Smithsonian Misc. Coll., vol. Si, No. 5, pp. 209-212. 



(b) Walcott, Smithsonian Misc. Coll., vol. 57, 1910-1912. 



(c) Davidson, British Fossil Brachiopoda, vol. S, 1883, p. 337. 



