696 W. C. ALDEN PRE-WISCONSIN GLACIAL DRIFT IN MONTANA 



and piling up in sharp knolls and ridges. This drift, however, overlaps 

 but little if any of the upper plain. Eastward from this point the 

 margin of the later drift gradually descends the eroded south slope until 

 in about 5 miles it lies 300 feet or more below the upland at the point 

 where the marginal moraine of the valley glacier swings off to the south- 

 ward across the valley plain. 



Mr. Calhoun^ also determined that the ice, though nearly filling the 

 valley of the North Fork of Cut Bank Creek, "did not spread over the 

 plateau to the north." 



Underlying this extensive high level plain is a yellowish to brownish 

 oxidized gravelly deposit like that described above, consisting principall}- 

 of quartzite with much green and red argillite, diorite, and some lime- 

 stone. The stones are subangular to rounded, and it seemed to me there 

 was no notable decrease in size with increasing distance from the moun- 

 tains. Numerous boulders 1 to 1^2 f^et in diameter are found 2 to 3 

 miles from the head of this plain and 8 to 10 miles from the mountains, 

 the source of all the material. That exposed in a ravine in the northeast 

 quarter of section 12, township 33 north, range 13 west, consisted of clay, 

 pebbles, and boulders mixed as in glacial till. In the southeast quarter 

 of this section 100 feet of unassorted material was found, and in the 

 northwest quarter of section 6, township 33 north, range 12 west, a 

 thickness of 150 feet was observed. Here and elsewhere glaciated peb- 

 bles were found, though these are nowhere abundant and consist mostly 

 of the green, quartzitic argillite. Such striated erratics were found in 

 the sides of the valley of Arnold Creek as far out on this plain as our 

 traverse was extended. 



It is the writer^s understanding that the deposit capping this Milk 

 Elver Eidge is included with what has been described as the "quartzitf 

 gravels" and has been regarded as pre-glacial in time of deposition. 

 Where seen by the writer, however, this contains well striated pebbles 

 and has the general characteristics of glacial drift. It evidently should 

 be correlated with the deposit of Two Medicine Eidge as pre-Wisconsin 

 glacial drift. 



Deposits on Saint Mary Eidge 



Emerging from the mountains between the bold salients known as 

 Divide Mountain and Singleshot Mountain, the waters of Saint Mary 

 Eiver flow in a general direction nearly due north through the lower lake 

 and beyond until they cross the international boundary. Bordering the 



® Loc. cit. 



