ORIGINAL ICE STRUCTURES IN SANDS 225 



The occurrence of these strikingly unlike deposits so closely inter- 

 related is a prominent feature. Conditions suitable for the hand- 

 ling of large bowlders and the accumulation of till cannot well 

 be regarded as consistent with thorough assorting and deposition 

 of finely stratified sands at the same time and place. 



The beds almost never lie flat; when they do it is only for a 

 few inches. They are almost invariably inclined toward the 

 north, northwest, or northeast; that is, against the general ice 

 movement as indicated by striae of the vicinity. Although the 

 maximum angle of repose for unconsolidated sands under sub- 

 aerial conditions is about 34 , the dips here commonly range from 

 io° through 20 , 30 , 40 , to 6o°. Inclinations of 68° and 71 

 have been observed and at one point, for a vertical height of four 

 or five feet, the beds are perpendicular or even slightly overturned. 1 



Occasionally contortion is observed 

 but only to a very limited extent. ^""^^^^_ / 



Faulting of several inches displace- ~~~/\ 



ment has been seen in such form that "^^-~__^__V7 \\ 



it could not possibly have happened /. 



by slipping on the growing margin of / --\_/ 



a delta deposit. In one instance the FlG - 3-— Small overthrust in 



i j -,i • 1 r ,1 r i, j- unconsolidated sands, thrust from 



beds on either side of the fault dip . , , ' 



1 a general northerly or north- 



away from the fault plane, on the westerly direction. 



one side at an angle of 67 , on the 



other side at an angle of 40 . In another instance a small thrust 



fault of an inch displacement was observed. It is of significance 



that the thrust was from the north (Fig. 3). 



In order to explain these occurrences and the ones to follow, it 

 may be assumed that the deposit was laid down near the margin 

 of the ice sheet. The material is so well assorted and the bedding 

 is so sharp that it is necessary also to conclude that the deposit 

 was originally water laid. Possibly the dips were originally toward 

 the ice sheet as they are now found, but the angles of inclination 

 could not have been as great as they are now. 



1 Similar structural features are noted by Professor T. C. Chamberlin in gravel 

 hills in Tippecanoe Co., Indiana. (" Hillocks of Angular Gravel and Disturbed 

 Stratification," A.J.S., XXVII [1884], 378-90.) 



