ECONOMICALLY IMPORTANT AQUEOUS DEPOSITS. 40o 



have been much as they are now, for near the northern end of the Duck 

 mountains there is a deposit of stratified silt underlying a great thickness 

 of unstratified till, and probably of inter-glacial age, holding numerous 

 fresh-water shells, with fragments of plants and fish remains essentially the 

 same as those living in Lake Manitoba and the surrounding lakes to-day. 



Karnes. — Very few kames have up to the present been definitely located 

 in the Canadian northwest, and none that would appear to have been con- 

 nected with any but the later stage of glaciation, viz., that of isolated local 

 glacial centres. The most important of these stretch as straight ridges down 

 the middles of deep valleys on the east side of the Duck mountain. The 

 two most important ones recognized were covered by several feet of pebbly 

 unstratified till, the same as that composing the surrounding hills. In some 

 cases what have been taken for moraines may possibly be kames, but it is 

 difficult in all cases to distinguish them in the absence of sections. 



Lacustral Beds. — Resting on the bowlder clay throughout very extensive 

 tracts in Manitoba and the North West territories are stratified sands, silts, 

 and clays that have been deposited in the bottoms of post-glacial or recent 

 lakes. The delineation of these lake basins is a work of the greatest economic 

 importance, as it is evident from what we at present know — that many of the 

 most fertile tracts in the west are underlain by rich alluvial clays deposited 

 in the bottoms of sheets of water of greater or less extent, which have now 

 disappeared. 



The number and extent of most of these old lakes has not as yet been de- 

 termined, but the positions of a few may be here generally indicated. 



The country drained by the upper waters of the Bow, Red Deer, and North- 

 Saskatchewan rivers, having at present a mean elevation of between two 

 and three thousand feet, was largely submerged, fine clays and silts over- 

 lying the till being here very generally met with, though no shore lines have 

 been recognized. A marked peculiarity of these deposits is the utter absence 

 in them of any shells or other fossils that would indicate the existence of 

 life in the lakes in which they were deposited. 



Another extensive stratified deposit skirts the eastern margin of the Mis- 

 souri Coteau. 



The depression lying west of the Duck mountain, which is now drained 

 southward by the Assiniboiue river, was also, at the close of the glacial 

 period, the basin of a large lake which first drained eastward through the 

 valley of Short creek and Valley river, between the Duck and Riding 

 mountains, and afterwards, when this valley was blocked by a local glacier 

 from the Duck mountain (the terminal moraine of which still stretches 

 across its western end), cut out the present valley of the Assiniboine. South- 

 ward, this lake extended down to lat. 51° N. Its northern and western 

 boundaries have not yet been determined ; but standing on the morainic 



L HI— Bull. Geoi,. Soc. Am., Vol. 1, 1889. 



