NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 223 



have been collected from only two localities, most of the Lower and 

 apparently all of the Middle Ozarkian being lacking. Our present 

 knowledge of the faunas permits a determination of boundaries for 

 the Ozarkian system in the region under discussion even though the 

 position of several formations is not yet fixed. 



Upper Boundary of Ozarkian 



Northern Cordilleran area. — A great disconformity is indicated at 

 the summit of the Ozarkian Mons formation in Alberta and British 

 Columbia. In the Glacier Lake (p. 338) and Clearwater Canyon 

 (p. T)2y) sections, the Sarbach formation overlies the Ozarkian, and 

 in the Ranger Canyon (p. 264) section the Sarbach, a thin bed of 

 shale, separates the Mons from the superjacent Devonian. At other 

 places various formations overlie the Mons, thus indicating tectonic 

 movements following the close of the Ozarkian. 



Southern Cordilleran area. — No sections have been clearly deter- 

 mined with a view to locating the upper boundary of the Ozarkian 

 in the Rocky Mountains south of Canada. In practically every 

 case, however, where Ozarkian is known there is no difficulty in 

 recognizing where it terminates, as the succeeding formations are 

 usually much younger and hence are readily distinguished. Every- 

 where throughout the Cordilleran area, further field-work must be 

 done in order to permit a proper solution of this as well as many 

 other stratigraphic problems. 



Lower Boundary of Ozarkian 



Briefly stated, the lower boundary of the Mons is marked by a 

 widespread and abrupt change in the character of the strata, and the 

 upper boundary by a change in the character of the limestones and 

 by disconformities produced by extensive changes in the sea bed that 

 resulted locally in non-deposition of sediments above the Mons. 



The outstanding feature of all of the sections where the contact 

 of the Upper Cambrian and Ozarkian is seen, is that the sediments 

 of the Upper Cambrian deposits were unlike those of the basal beds 

 of the Ozarkian and that, with the exception of the Tilted Mountain 

 locality, very few fossils have been found in the upper layers of the 

 Cambrian, while the basal layers of the Ozarkian usually contain an 

 abundant fauna. 



Northern Cordilleran area. — The Ozarkian Mons formation in the 

 Saskatchewan and Sawback areas usually has at the base more or 

 less argillaceous shale with layers of gray limestone and interforma- 



