clay, 

 andf 



6 Scientific Intelligence. 



It the section of materials exposed in the bluff upon the lake shore 

 wholly Post-tertiary. It consists of intimately mingl 



ifusedly stratified above, horizontally stratified lower down, 

 followed downward by an increase of argillaceous material and 

 pebbles, interrupted by a bed of bowlders, beneath which for 10 feet 

 is a mass of bowlder clay seen above a lake-border talus of ten feet. 



aula, there should lie, still lower, a thick bed of tine, horizontally- 

 stratified clay, with few pebbles, resting on a bottom-sheet of peb- 

 bles and bowlders. The drift here is presumably not less than 300 

 feet thick. Now it is possible that, 2,500 feet back from this blufi; 

 the bed-rock should appear at the surface : but my experience in 

 Michigan strongly inclines me to believe that such is not the fact ; 

 and that hence, the numerous outcrops near the lake are mere de- 



We have, then, in Michigan, in regions widely separated, the well- 

 established phenomenon of extensive tabular masses of limestone 

 floating in the midst of semi-stratified sands, generally believed to 

 have been moved and deposited by an aqueous action, which, ob- 

 viously, could not have transported at the same time these enor- 

 mous tables of rock. We have, in addition, in some parts of the 

 State, the evidence that this action was sometimes exerted in a 

 northerly direction. Geological theory must attempt to account for 

 these facts. 



The generally accepted doctrine of continental glaciation, recog- 

 nizes a time when the broad glacier underwent a rapid dissolution. 

 The volume of water arising is believed to have been sufficient to 

 produce a long-continued, torrential flood, which moved and as- 

 sorted whatever detritus existed in its path. Disregarding the 

 detrital material, which must have originated from atmosph^'ric, 

 pluvial and fluvial action over the preglacial surface, a vast volume 

 of detritus must have been originated during the prevalence of the 

 glacier, and chiefly through its action. Most of this must have 

 rested at or near the bottom of the glacier ; but probably no small 

 portion had become incorporated with the ice, or intruded into its 

 fissures, or deposited upon its back. The first glacial film embraced 

 the original projections of the ancient surface, which, with the move- 

 ment of the glacier, must have been displaced to become ultimately 

 a part of the glacier debris. These and the materials derived from 

 sub-glacial detrition must have found their way, to some extent, 

 into the bottom crevasses caused by any diminution in the steep- 

 ness of the slope down which the glacier moved, and still more 

 when, as was often the case, the change of slope became, in reality 

 a northward declivity. These ordinary conditions of the conti- 

 nental glacier— but feebly represented in the steeper slopes and 

 narrowed limits of modem glaciers— must have resulted frequently 

 in extensive disruptions of the ice, faintly typified in the pyramids 

 and seracs of the Alpine ice-streams. Such upheavals of the lower 

 beds— still more, occasional complete overturnings of portions 

 of the glacier, must have brought considerable earthy detritus to 



