CAMBEO-SILUEIAN OF MANITOBA. 83 



a much smaller shell (the maximum diameter of the type of that species being only a little 

 over six inches) its aperture is broadly reuiform, with a lateral diameter nearly double that 

 of the dorso- ventral, its volutions have no veutro-lateral angulation, and its suturai lines 

 are nearly straight, not only on the sides but also upon the abdomen or venter. 



The exact stratigraphical relations of the subdivisions of the Cambro-Silurian rocks of 

 Manitoba have yet to be ascertained. On purely palseontological evidence, the highly fossili- 

 ferous deposits at Stony Mountain w^ere referred to the Hudson River formation by the 

 present writer, in 1880,' and the fossils of the pale bulf-coloured limestones or dolomites 

 of East Selkirk and Lower Fort Garry have long been supposed to show that these rocks 

 are the equivalents of the Galena limestone or upper portion of the Trenton formation, of 

 Wisconsin and Iowa. On the same evidence, the somewhat similarly coloured and 

 fossiliferous limestones of the islands and shores of Lake Winnipeg, appear to be of the 

 same age as the Trenton Limestone proper, or, at any rate not older than the Birdseye and 

 Black Eiver Group of Eastern Canada and the State of New York. It is possible that 

 the fossiliferous rocks on the shores and islands of Lake Winnipeg may be a little lower 

 down in the series than those at East Selkirk and Lower Fort Garry, but the whole 

 of these deposits, apart from those at Stony Mountain and elsewhere in Manitoba which 

 can be somewhat confidently referred to the Hudson Eiver group, probably represent 

 only one well defined horizon in the Cambro-Silurian system. However this may be, in 

 the writer's judgment, there is at present no satisfactory palteontological evidence for the 

 existence of the Chazy formation or its equivalent, in Manitoba. 



Geol. Suiv. Can., Itep. Progr., 1878-70, p. 50 c 



