238 T. C. CHAMBERLIN 



tinuous) had forced itself over the edge of this debris. The 

 result was the bending upwards of the edges of the layers of the 

 Bowdoin glacier. Accompanying this there was a phenomenon 

 which seemed at the time to be a clear and unequivocal expres- 

 sion of the shearing of these layers over each other, due to the 

 resistance of the morainic material. Subsequent studies, as else- 

 where remarked, led to some skepticism as to the validity of 

 this interpretation. This point was not visited after the skep- 

 tical spirit arose, and hence I am only able to reproduce the 

 observations and interpretations as they impressed themselves 

 at the time. On the nearly vertical face of the glacier where it 

 was most strained in being thrust over the morainic mass, there 

 were as many as nine distinct projections of upper layers over 

 under layers. The over-projection was sharp and definite and 

 at once attracted the notice of my companion, Mr. E. B. Bald- 

 win, who called my attention to it. The ground for skepticism 

 regarding the interpretation of phenomena of this class is the 

 presence of debris bands which may give rise to differential 

 melting. There is no question that projections of a kind much 

 like those here observed are due to such unequal melting. It 

 seems to be demonstrable also that overthrust shearing takes 

 place in this way. Each case must therefore be judged by 

 itself. The limited amount of debris in this glacier encourages 

 less skepticism regarding overthrust here than in some other 

 cases. My notes state that pebbles and bowlders were some- 

 times lodged between these layers and that they appeared to 

 have been pushed along the face of the layers in the shearing 

 process, sometimes making grooves in the ice. Both notes and 

 memory imply scantiness of debris between the layers. Unfor- 

 tunately my photographs at this point were not a success. The 

 overjutting of the layers ranged from a few inches to eighteen 

 inches. They were most pronounced where the strain resulting 

 from the obstruction would naturally be greatest and they died 

 away in either direction. At another point somewhat farther 

 on the phenomenon was repeated, but here there were but five 

 chief planes of displacement in the vertical section. The maxi- 



