202 T. C. CHAMBERLIN — ^^GLACIAL STUDIES IN GREENLAND. 



rounded by basalt and sandstones. About Inglefield gulf the gneissic 

 series is covered by thick terranes of sandstone and shale which are 

 traversed by basic dikes. The clastic series forms but a border, and is 

 only reached by the ice near its edge. It is thus possible to tell how late 

 the erratics from it were introduced into the ice, what courses they pur- 

 sued, and what actions they suffered. 



The Effects of Latitude on Glaciation. 



In so far as latitude is merely an agent of glacial temperatures, it is 

 not necessary to consider its effects, for some equivalent cause of glacial 

 temperatures must have been operative in Pleistocene times. It is only 

 the distinctive results, such as may be attributed to the constancy of the 

 sun above or below the horizon, the low angle of incidence of its rays, 

 their impact from all points of the compass, and similar features, which 

 need to be considered. 



A partial means of determining what these are is found by comparison 

 between the glaciers of Disco island, only a little within the Arctic circle, 

 and those of Inglefield gulf, 8J degrees farther north. The Disco glaciers 

 seem to have all the familiar characteristics of glaciers south of the Arctic 

 circle, while the Inglefield glaciers take on habits significant of their 

 high latitude. This will appear as we pass on. 



Verticality of the Glacial Margin. 



The feature which is likely first to impress the observer, on reaching 

 the glaciers of the north, is the verticality of their walls. Southern gla- 

 ciers, as you are aware, terminate in curving slopes, and the Disco glaciers 

 of middle Greer^land have the same habit ; but the margins of the Ingle- 

 field glaciers rise abruptly like an escarpment of rock, lOO or 150 feet or 

 more. The layers of ice are cut sharp across, exposing their edges. This 

 verticality has been observed by Greely, Heilprin and others. It is not 

 quite universal, however, as sloping forms occur here and there. Occa- 

 sionally a glacier presents both aspects. These abrupt terminal walls 

 turn toward all points of the compass. It is perhaps too much to say 

 that they do this indifferently, as but few glaciers facing the north were 

 seen, but among these verticality prevailed much as elsewhere. (Figures 

 1 and 2, plate 3.) 



The cause, with little doubt, is the low inclination of the sun's rays and 

 their impact from all points of azimuth in succession. Rays of low slant 

 strike the back of a glacier at a very acute angle and glance away with the 

 greatest facility and the least effect. On the edge of the glacier, however, 

 they strike more vertically and effectively. In addition to this, the slanting 



