TERMINAL MORAINES. 217 



lower land ; the flow of water from the ice probably having 

 carried away the debris as rapidly as it was pushed forward by 

 the ice. On the other hand, in case the loop was pushed up 

 an inclined plane, and the water did not find free escape, it 

 (the loop) is well developed all around. The outer moraine in 

 some places is very rough and stony ; at other points it is a 

 smooth, broad ridge, with few knobs, and covered with a deep, 

 fertile soil.* 



Dr. G. M. Dawson early discovered the significance of 

 this great Missouri coteau in its extension north of the 

 United States boundary-line, and thus describes it : 



On approaching its base, which is always well defined at a 

 distance, a gradual ascent is made, amounting, in a distance of 

 twenty -five miles, to over 150 feet. The surface at the same 

 time becomes more markedly undulating, as, on nearing Turtle 

 Mountain from the east, till almost before one is aware of the 

 change, the trail is winding among a confusion of abruptly 

 rounded and tumultuous hills. They consist entirely of drift 

 material ; and many of them seem to be formed almost alto- 

 gether of bowlders and gravel, the finer matter having been to 

 a great extent washed down into the hollows and basin-like 

 valleys without outlets with which this district abounds. The 

 ridges and valleys have in general no very determined direc- 

 tion, but a slight tendency to arrangement in north-and-south 

 lines was observable in some places. 



The bowlders and gravel of the coteau are chiefly of Lau- 

 rentian origin, with, however, a good deal of the usual white 

 limestone and a slight admixture of the quartzite drift. The 

 whole of the coteau belt is characterized by the absence of 

 drainage valleys ; and, in consequence, its pools and lakes are 

 often charged with salts, of which sulphates of soda and mag- 

 nesia are the most abundant. The saline lakes frequently dry 

 up completely toward the end of the summer, and present 

 wide expanses of white efflorescent crystals, which contrast in 



* " Proceedings of the American Association for the Advancement of Sci» 

 ence," vol. xxxiii, 1884, p. 383. 



