Shaler.] 36 [February 6» 



for record of which see a short but suggestive article by him in 

 vol. 22 of these Proceedings, page 201. 



In relation to the rounded and pebbly forms of the quartzite as 

 found in the conglomerate of the Boston basin it can be said that 

 this may have been and probably was largely due to the abrasive 

 action of the waves after subsidence. 



In hope of throwing some light on the relative position of the 

 rocks of the basin, I was led to think of their origin, and not 

 believing the boulders and pebbles of the conglomerate to have 

 been the result of water erosion alone I came to the conclusion 

 that they were mainly the unchanged material (I mean unchanged 

 by chemical forces) of the ancient formations existing in the 

 strata that became submerged through igneous action within the 

 area of the basin. This view of the probabilities of the past 

 may be and likely is far from a correct one in all particulars, and 

 yet I think it may be found worthy of consideration. 



ON THE ORIGIN OF KAMES. 



BY N. S. SHALER. 



The various classes of drift-deposits formed during the glacial 

 period afford some of the most puzzling structures with which 

 the geologist has to deal. Some of these deposits are, it is true, 

 quite readily interpreted. The broad sheet of ground moraine 

 that covers the general surface of glaciated countries is clearly 

 the wreckage left by the ice when it melted. The drift terraces 

 that border the sea, the great lakes, and the rivers are the 

 rearranged waste of terminal and ground moraines. The strong, 

 rampart-like ridges of intermingled sand, gravel and boulders, 

 having a general east and west extension, are readily seen to 

 fall into the class of front moraines comparable in a general way 

 to the terminal heaps of the Swiss glaciers. But there still remain 

 two classes of drift-deposit that await interpretation. These are 

 the lenticular hills or drumlins, and the class of gravel deposits 

 known as Karnes or Eskers, often called in America Indian ridges. 

 I propose in the following pages to discuss the origin of the 

 last named class of structures. 



