56 OSCAR H. HERSHEY 



overrides the deposit, if the basal friction is great enough, it will 

 turn up the strata in contact with it, twist them over on to the as 

 yet undisturbed strata, and inaugurate a motion in the mass 

 which may be not inaptly compared to the movement of a roller 

 under a heavy weight. Rarely, however, will the actual action 

 be as perfect as it should theoretically be, but usually there is 

 combined with the rolling process a forward and downward 

 thrust which crushes the mass. The more resistant portions of 

 the ledge break into huge angular blocks, the semi-decayed lay- 

 ers into smaller fragments intermingled with a great quantity of 

 calcareous sand. The rolling is obviously produced by the 

 "drag" of the forwardly moving glacier, while the thrust is the 

 result of its great weight. This kneading process is not only 

 theoretically probable, but has given rise, as I have already 

 intimated, to phenomena in Stephenson county, Illinois, which 

 are explainable only under the supposition of having been pro- 

 duced by its action. 



6. By a continuance of the kneading process, the larger 

 blocks are crushed, all evidences of the original lines of stratifi- 

 cation are destroyed, and the deposit for the first time bears a 

 slight resemblance to certain very stony tills. Few of the par- 

 ticles are smaller than the crystals of which the original lime- 

 stone was composed, and, therefore, the deposit may still be 

 clas'^ed with the "transported rock ledges." Moreover, in 

 this stage there are practically no foreign rock fragments 

 although a few Canadian pebbles may be found imbedded in it 

 far from the surface, proving its glacial age.' 



7. The process of manufacture between the last stage and 

 the typical glacial till may proceed along several lines, all simi- 

 lar in the general features of the method, but differing in details. 

 Several deposits along the Galena road, one mile northwest of 

 Freeport, and along the C. G. W. R. R. between German Valley 

 and Egan, seem <-o represent a stage slightly in advance of that 

 just described. Here the angular limestone debris is com- 



' A deposit representing tiiis stage is finely exposed in a gravel pit, one mile north 

 of Freeport, where the angular gravel overlies water-worn drift gravel. 



