268 ALCOCK AND BRUCE PRECAMBRIAN ROCKS OF MANITOBA 



been derived from two types of exploration, namely, track surveys with 

 geological notes, performed by Bell, Cochrane, Tyrrell, Bowling, and 

 Mclnnes, and more detailed geological surveys made during recent years 

 in the areas where active prospecting for minerals has been carried on. 

 It is the object of the present paper to correlate as far as possible the 

 more recent information which has been obtained. No attempt is made 

 to apply the nomenclature adopted for the pre-Cambrian succession of 

 any of the geological subprovinces along the southern border of the Cana- 

 dian shield, and the only comparison offered is with the succession found 

 in the Kainy Lake area of Ontario — a region which is geographically the 

 nearest and geologically the most similar of any area outside the Province 

 of Manitoba where detailed work has been done. It is also not to be as- 

 sumed that the paper is a final statement of all the problems connected 

 with the pre-Cambrian geology of Manitoba. Complete detailed work has 

 been performed as yet in but few places, and future investigation will 

 doubtless bring to light many new facts. The following discussion is, 

 therefore, merely an attempt to collect, in summarized form, our present 

 knowledge of the pre-Cambrian history of the province. 



General Character op the Country 



. The southwestern part of Manitoba, underlain by flat-lying Paleozoic 

 and Cretaceous strata, is separated from the norrtheastern part, of Ordo- 

 vician and Silurian rocks lying in the James Bay basin, by a broad band 

 of pre-Cambrian rocks which occupies three-fourths of the province. A 

 few outliers of Ordovician dolomite are found in front of the low, irreg- 

 ular escarpment that marks the contact of the Paleozoic rocks of the 

 southwestern section with the lower lying pre-Cambrian formations. The 

 northeastern contact is in most places hidden by glacial and postglacial 

 deposits. 



The surface of the pre-Cambrian ])elt slopes gently from an elevation 

 of about 1,200 feet in the western part of the province eastward to Plud- 

 son Bay. It presents the features so uniformly developed over the entire 

 Laurentian- plateau, the two most important of which are low relief and 

 disorganized drainage. Only in few places do elevations rise more than 

 100 feet above the adjacent lakes and valley bottoms, and hills of greater 

 height are prominent landmarks. In detail, however, the surface of the 

 country is very irregular, consisting of low broken ridges separated by 

 depressions in which lie lakes and muskeg swamps. The rivers are suc- 

 cessions of lake expansions connected by streams with rapids, waterfalls, 

 and, in places, narrow gorges. The lakes have many islands, and long, 

 narrow bays give them a great length of shoreline in comparison to their 



