OJATA BEACHES IN NOETH DAKOTA. 461 



a very flat and almost level surface of till, witli alkaline soil, extends east- 

 ward. The top of the escarpment is capped to the depth of a few feet with 

 beach gravel and sand, at 877 and 880 feet, deposited during the upper 

 Ojata stage of the lake, and the erosion of the steep sloj)e below may have 

 been accomplished mostly during a lower and later portion of this stage. 

 Abetter interpretation, however, seems to be found in attributing the upper 

 gravel to the highest iluctuation of the lake when raised several feet by the 

 rapid glacial melting in the sunnner, the till below having been cut away 

 by the reduced water level in the winters, when it was lashed into powerful 

 waves by storms. 



But a large share of the erosion of the less steep lower slope was done 

 by the lake dm-ing the lower Ojata stage. In the latest and lowest portion 

 of that stage there was also formed a discontinuous beach ridge of gravel 

 and sand, which lies in isolated, irregular accumulations a half mile east of 

 the escarpment, and rises 6 to 8 feet above the flat expanse on each side, 

 with crests at 870 feet, approximately. This fragmentary beach divides a 

 tract of till on the west which has suffered much erosion of its surface, being 

 therefore strewn with frequent or abundant bowlders, from another tract on 

 the east, where the upper part of the till to the depth of 5 to 10 feet or more, 

 still lying as it was deposited in Lake Agassiz, bears marks of imperfect 

 stratification, and has fewer bowlders and less gravel on the surface than at 

 a slight depth. Within 10 to 15 feet beneath the surface, as shown by 

 wells and the ravines of streams in the neighborhood of Ojata, the lacus- 

 trinely modified till, which was englacial, is succeeded below by the wholly 

 unstratified ground moraine. It is also to be noted that a thin layer of 

 lacustrine clayey sand and fine silt, doubtless derived chiefly from the ero- 

 sion of the escarpment on the west, is spread with a thickness varying from 

 a few inches to a few feet on much of the surface eastward from the lower 

 Ojata beach. 



Ten to 15 miles northwest of Ojata the upper one of these two shore- 

 lines is well-marked in Gilby by a typical beach ridge of gravel and sand, 

 lying on or near the eastern limit of the till, be}'ond which lacustrine and 

 alluvial silt stretch east to the Red River. Mr. John Clilby's house, in the 

 southwest quarter of section 22, is built on the gravel beach, which thence 



