TILL OVERLYING THE ESKER GRAVEL 415 



"Some two hundred boulders were found scattered upon the area of the ex- 

 cavation ; and they occur with nearly the same frequency on other portions of 

 this northern slope of the hill, but are rarely found on its top and southern 

 slope. They vary in size from 2 to 8 or 10 feet in length; nearly all are 

 Archean, but a few of Paleozoic limestone, up to 5 feet in length, were ob- 

 served. None was seen inclosed within the gravel and sand of the esker, and 

 the workmen informed me that they occur only on or near the surface. This 

 hill was covered by Lake Agassiz, and its boulders were doubtless dropped or 

 stranded from bergs and floes on this lake before the border of the ice-sheet 

 had retreated from the vicinity. Indeed, the occurrence of the boulders chiefly 

 on the northern slope seems to indicate that they were mostly stranded there 

 while ice yet remained beneath this deposit and prevented its entire sub- 

 mergence in the lake." 



Details of the esker section and the overlying till on the deeper south 

 side of the excavation are as follows : 



From its west end this section has a thin covering of till, with fre- 

 quent boulders 2 to 5 feet in diameter, for a distance of about 350 feet. 

 In the east half of this extent the till varies from 2 to 8 feet in thick- 

 ness, being thickest near its east limit, where it ceases by the rising of 

 its low^^er boundary at an angle of about 45 degrees to the surface. Above 

 the till along most of this extent, excepting where it comes to the sur- 

 face at the east, is a thin surface deposit of gravel 1 to 3 feet thick. 

 The till is underlain by the very coarse water- worn esker gravel, ob- 

 scurely and confusedly bedded, 10 to 20 feet thick and continuing below 

 the excavation. 



About 5 to 10 feet east from the limit of the till is a sand mass, 3 by 

 () feet in dimensions, lying 2 to 6 feet below the surface, wholly inclosed 

 in the coarse gravel, being perhaps a frozen mass there imbedded while 

 tlie gravel was rapidly deposited around it. 



Through the next 100 feet east the section is mostly very coarse gravel, 

 not distinctly bedded, with pebbles and cobbles up to 8 inches in diame- 

 ter, well water-worn, and also inclosing occasional partly or wholly angu- 

 lar rock fragments up to 18 inches in diameter, from the surface down- 

 ward, seen to the depth of 20 feet. In that part, between 30 and 60 

 feet east of the limit of the till before noted, the gravel incloses an irregu- 

 lar inclined layer of sand, 6 inches to 3 feet thick, beginning at the 

 surface and running downward to the east 12 feet in its length of 30 

 feet. This is the only exception to the coarse gravel otherwise making 

 all that part of the section. 



Next east for 75 feet the section, 20 to 25 feet deep, is finer gravel, 

 with pebbles up to 4 or 6 inches in diameter, containing no unworn 

 larger fragments; but there it is capped by a stratum, 2 to 5 feet thick, 



