206 T. C. CHAMBERLIN— GLACIAL STUDIES IN GREENLAND. 



differentiates the accumulating snow. In view of these varied agencies 

 of stratification, it is doubtful if we can look with any confidence for 

 criteria by which the annual snowfall can be safely distinguished from 

 that of other periods. 



The original stratification could not have been verj^- pronounced. 

 Perhaps it was intensified somewhat during subsequent consolidation, 

 but some new agency was necessary to produce the more definite part- 

 ings and to introduce the layers of debris. This agency appears to have 

 been a shearing movement between the layers. On almost every one of 

 the vertical faces certain laj^ers jut out sharply over those', beneath. 

 Sometimes there are six, eight or ten of these projections, one above 

 another, ranging from a few inches to one or two feet. In rare cases th© 

 projection reaches eight, ten or fifteen feet. At first sight this seemed 

 clear proof of a shearing motion,* but upon more critical study it was 

 ascertained that there was usually earthy matter in tlie upper part of the 

 under layer which caught the sunlight and was melted back faster than 

 the pure ice above, and suspicion arose that the whole phenomenon might 

 be attributed to differential melting under the influence of the very 

 oblique rays of the sun. In following a given projection laterally, it often 

 terminated where the earthy impregnation ceased. Of course, the shear- 

 ing and the impregnation might have been companion phenomena due 

 to a common cause, but the observation gave ground for doubt as to the 

 trustworthiness of this class of evidence. More direct proof was sought 

 in the grooves or flutings, which it was supposed erratics, lying in the 

 junction or inequalities of the layers, might produce. The search met 

 with apparent success. Fluted surfaces were found. The under sur- 

 faces of many of the overprojecting beds were fluted, and, at first sight, 

 this seemed to give abundant and incontestable evidence of shearing, but 

 here again more careful study made it appear quite certain that much of 

 this fluting was due to the water which trickled down the face of the 

 overlying layer. Instead of dripping freely away when it reached the 

 edge of the ice-cornice, it followed the under surface backward and fluted 

 it. In most cases I could not tell whether the fluting had been initiated 

 by shearing and merely developed by the water or not. In searching 

 for fluting not attributable to water-action I found instances where the 

 junction-plane marked by debris was itself fluted, the earthy material 

 passing backward between the layers in a corrugated form. 



Another class of evidence was found in the fallen blocks of stratified 

 ice which had entered upon the initial stages of disintegration sufficiently 



* The term "shearing" is used in this discussion in its common mechanical sense, signifying 

 differential movement along a plane, and not in the ultra-physical sense, which embraces ail move- 

 ments of particles upon each other, even those of liquids and gases. 



