1885.] NATURAL SCIENCES OF PHILADELPHIA. 157 



MARGINAL KAMES. 

 BY II. CAKVILL LEWIS. 



Introduction. — During the course of an investigation, in 1881, 

 of the extreme southern edge of the great ice-sheet in Pennsyl- 

 vania, as marked by its terminal moraine, the writer had an 

 opportunitj 7 " of studying several phenomena produced by the 

 glacier along the line of its southern terminus ; one of the most 

 interesting of which phenomena were certain short hummocky 

 ridges of stratified drift, which, often closely connected with the 

 terminal moraine, appear to belong to a class of surface deposits 

 elsewhere called Karnes. 



The kames of Scotland, the Eskers of Ireland, and the Asar, 

 or osars, of Scandinavia, all closely related, if not identical, 

 deposits, find an analogue in the ridges of stratified drift which 

 have been described by a number of geologists as occurring in 

 northeastern America, including Canada. 



They may be described as narrow ridges of stratified, water- 

 worn, generally sandy drift, which, sometimes forming a series 

 of tortuous and reticulated hills, sometimes a nearly regular 

 straight ridge, and often forming knob-like conical hills (" hum- 

 mocks "), alternating with similar conical depressions ("kettle- 

 holes "), generally lie along valleys or depressions, and have a 

 general downward slope from a higher to a lower level. 



These gravel ridges are generally quite steep — as steep often 

 as the nature of the material will allow. This steepness is quite 

 striking to a geologist accustomed to the gentle slopes of the 

 gravel formations in the non-glaciated portion of this country, 

 and at once suggests the recency of their origin. 



The internal structure of kames is in general anticlinal. 

 " Flow-and-plunge " structure, and oblique lamination, the evi- 

 dence of rapid fluviatile action, is often seen in their interior; 

 and as a rule the material is finest in the interior, and most 

 coarse on the exterior portions of the kame. 



Wherever along the course of the terminal moraine the writer has 

 had an opportunity of examining recently made transverse sections 

 of these drift ridges, he has found clean water-worn sand within, 



1 Read before the British Association for the Advancement of Science, 

 Montreal, August 29, 1884. 



