396 .1. B. TYRRELL — POST-TERTIARY DEPOSITS OF MANITOBA. 



M amain.-. < Iretaceous or Tertiary beds everywhere underlie the post-Tertiary 

 or recent deposits. The character of most of these bed-, which consist of 

 sandstones, marls, and clay-shales, is perfectly well known, but I wish to 

 draw your attention for a moment to the occurrence of conglomerates of 

 Miocene and Pliocene age, the existence of which has been pointed out of 

 [ate years, since they furnish sources of supply for a large amount of drift 

 which was formerly supposed to have been derived directly from the Rocky 

 M luntains at the same time that the other associated portions of the drift 

 were derived from the Axchean and Paleozoic rocks to the east. 



The Miocene is at present known as a fresh-water formation of -and-. 



silts, and gravel, or ( glomerate, lying on the eroded surface of the Creta- 



U8 and Laramie rocks on the more elevated portions of the Hand ami 

 Cypress hills, and on the higher plateaus stretching east from these as far as 

 long. 1 (, 7- 1-Y. The pebbles in this conglomerate are all well rounded and 

 waterworn, and consist of a white quartzite similar to that in the Rocky 

 Mountains described by Mr. McGonnell as belonging to his"Bow River 

 group," or lower portion of the Cambrian system. This material has been 

 carried eastward by rapid streams during Miocene times, and deposited either 

 in lake- or on the flood-plains of rivers. The gravel has in many pla 

 been indurated by the infiltration of a calcareous cement into a hard con- 

 glomerate, much harder than the underlying -hales and sand-tone-, and has 

 preserved the hills that it now covers from degradation by atmospheric and 

 fluviatile agencies to the Bame extent as the surrounding country, and at the 

 same time has furnished a scale by which to measure the thickness of the 

 rocks washed away since Miocene time-. 



The Pliocene, here called by Mr. McConnell the "South Saskatchewan 

 group," is al-o composed of rounded quartzite gravel : but it now occupies the 

 bottoms of valleys or other depressions, and has been derived in part from 

 the pre-existing Miocene deposits, and also in part directly from the quartzite 

 area- of the mountains. 



The district under consideration, extending from the boundary between 

 the United State- and Canada northward to the North-Sa-katchewan river. 

 i- largely overlain by a series of heterogeneous deposits which are commonly 

 embraced under the term " drift." Tin- consists of bowlder clay or till. 

 morainic detritus including erratics, drumlins, kames, alluvial sands, clays, 



and -ilt-, beach-ridges, terrace-, etc. 



Tin. ( ii LCI \i. Mi POM i-. 



Till. -The bowlder day <»r till rests irregularly on all the pre-glacial 

 formations down to the fundamental gneisses and schists, and in the A.rchean 

 area itself fills many protected depressions and recesses. I i - not. how- 



r, reach the base of the Rocky Mountains, but extends westward to within 



