Analytical Abstracts of Current 

 Literature.' 



The Sub -Glacial Origin of Certain Eskers. By William Morris 

 Davis, Harvard University. (Proceedings of the Boston Society 

 of Natural History, Vol. XXV., May i8, 1892). 



A critical discussion of the conditions under which it is conceived certain 

 eskers and sand plateaus (plains) were formed. The Auburndale district, 

 ten miles east of Boston, presents three classes of modified drift deposits; — 

 sand plateaus, eskers, and kames. These deposits are well exposed. 



The sand plateaus have the characteristics of delta deposits of glacial 

 streams, — even surfaces, well -bedded sands and gravels, the beds sloping out- 

 ward from the "head" at an angle of 12° to 20-, and in close agreement 

 with the slope of the plateau front, a lobate margin, deposits distinctly coarser 

 at the head than near the front, and a series of nearly horizontal roughly 

 cross -bedded gravels overlying the sloping beds. 



The eskers are essentially of the same material as that of the plateau, 

 often so poorly stratified as to render differentiation of the beds difficult. The 

 interstices between the pebbles are often unfilled, although there is abun- 

 dance of fine material in adjoining layers. This "open work" is taken to 

 indicate rapid deposition, and seems to preclude the supposition that the 

 gravels have settled down from a superglacial position, or been traversed by 

 currents of any volume. In several instances the eskers can be followed to 

 direct union with sand plateaus. Towards its lower end the esker frequently 

 "gives out branches" and "the adjacent lowland surface becomes more or 

 less encumbered with sand mounds or kames," indicating a decayed margin 

 of the ice. 



Prof. Davis' conclusions are : 



"I. The eskers and sand plateaus of Auburndale and Newtonville were 

 formed by running water just inside and outside of the ice margin in the 

 closing stage of the last glacial epoch. 



"2. The ice -sheet was a stagnant, decaying mass at the time of their 

 formation, as is shown by the ragged outline of its margin. 



' Abstracts in tnis number are prepared by Henry B. Kummel, Chas. E. Peet, 

 J. A. Bownocker. 



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