384 W. A. Johnston — Sedimentation in 



deposition in brackish water. The Champlain (late 

 Pleistocene) clays in the Ottawa basin are in places well 

 banded. The banded clay rarely if ever contains marine 

 fossils and was probably deposited in nearly fresh water. 

 The clays containing marine fossils, and therefore depos- 

 ited in salt water, are not definitely banded. 



Seasonal handing in glacial clays. 



De Geer holds that the banding of the late glacial clays 

 is seasonal in character, — the coarser part of the band 

 being the summer deposit and the finer part the winter 

 deposit, — that the banding is due to the fact that glaci- 

 fluvial rivers entering a lake or an only slightly brackish 

 inland-sea have followed its bottom, being heavier than its 

 water, and that this is clearly shown by the current-bed- 

 ding and sand interbedded with the clay ; whereas in the 

 case of streams entering the sea, the river water flows 

 out on the surface and can only transport the finest clay, 

 the coarser sediment being dropped near the shore or ice- 

 border, thus giving rise farther out to an almost unlami- 

 nated clay. 7 



In the case of Lake Louise, it does not appear, as 

 already pointed out, that appreciable currents follow the 

 bottom. It is well recognized that the great mass of the 

 waters of the glacial lakes of Late Pleistocene time must 

 have been at the temperature of maximum density 

 through the year, and as silt and clay in suspension only 

 slightly affect the density of the water, — unless the silt 

 is large in amount and extremely finely divided — it seems 

 improbable that appreciable river currents could have 

 followed the bottoms of the lakes, except possibly under 

 certain conditions. In places where the glacier termin- 

 ated in a lake or inland sea and streams under hydrosta- 

 tic pressure issued from the glacier, at some depth below 

 the surface of the water, it is possible the river currents 

 would continue for some distance along the bottom, if 

 the density of the river water was slightly greater than 

 the lake water. If the water body into which the stream 

 flowed was brackish, the river water would be forced to 

 rise to the surface because of its less density. The sand 



7 Opus cit. p. 250. 



