614 G. M. DAWSON ON THE SUPEEFICIAL GEOLOGY OF 



areas of gently undulating land, though always characterized by the 

 abundance of pools and swamps. Notwithstanding the apparent 

 abundance of water, there are few brooks or drainage-valleys, and 

 the streams which do occur are quite small. The surface seems 

 very nearly that of the drift as originally deposited, though sufficient 

 fine material has been washed from the ridges to render the inter- 

 vening hollows flat-bottomed. 



Edge of the Third Prairie- Plateau. 



One hundred and twenty miles west of Turtle Mountain the second 

 prairie-plateau comes to an end against the foot of the great belt of 

 drift deposits known as the Missouri Coteau. Beyond this point 

 three diverse zones of country cross the forty-ninth parallel ob- 

 liquely with a west-north-west course, in the order subjoined : — 



1. Tumultuously hilly country based on a great thickness of 

 drift, and forming the Coteau de Missouri properly so called. 



2. Flat-topped watershed plateau, formed of rocks of the Lignite 

 Tertiary, and constituting a part of the first transverse watershed 

 already described. 



3. Lower, broken-down region, south of the plateau, partly based 

 on the Lignite Tertiary, and characterized by gorges and large 

 valleys draining towards the Missouri. 



The second region can perhaps hardly be said to cross the line, 

 but appears immediately north of it. On the line and southward 

 the streams flowing to the Missouri rise near the southern edge of 

 the first division, the greater part of the plateau having succumbed to 

 denuding agencies. 



The Missouri Coteau (fig. 2, and Map and section PI. XXXII. , z) 

 is one of the most important features of the western plains, and is 

 certainly the most remarkable monument of the Glacial period now 

 existing there. I have had the opportunity of examining more or 

 less carefully that portion of it which crosses the forty-ninth parallel, 

 north-westward for a length of about 100 miles. On the parallel, 

 the breadth of the Coteau, measured at right angles to its general 

 course, is about 30 miles ; and it widens somewhat northward. 



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

 tance, a gradual ascent is made, amounting in a distance of 25 

 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 altogether of boulders 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 dis- 

 trict abounds. The ridges and valleys have in general no very 

 determined direction; but a slight tendency to arrangement in north- 

 and- south lines was observable in some places. 



The boulders and gravel of the Coteau are chiefly of Laurentian 



