TESTS OF SUBGLACIAL OE. SUPERFICIAL DEPOSITION. 425 



was deposited by a superficial stream as it plunged into a pool beneath tlie 

 ice, or by a stream that was wholly subglacial. 



MBANDERINGS OF A RIDGE. 



For convenience, the meandering's may be divided into two classes. 



Meanderings of the first class are deflections for several or many miles, 

 such as all the longer osars and osar-plains of Maine make in order to fol- 

 low valleys or to find a low pass through the range of hills. Many of the 

 longer deflections along valleys are where the ice was also deflected and 

 the osars are pai-allel to the glacial flow. Such places would be favorable 

 to the formation of subglacial tunnels. Other long meanderings are found 

 in level regions where the direction of ice flow would be substantially the 

 same over all the plain. If subglacial tunnels were here formed, it must 

 have been for a part of the distance transverse to the direction of glacial 

 flow. The Seboois-Kingman-Columbia osar leaves the valley of Seboois 

 River, a tributary of the Penobscot River, and takes a course for 20 miles 

 southeastward over two divides to Patten. It here abandoned a north-and 

 south valley, down which the ice could freely flow, for a course transverse 

 to the motion of the ice. Here the course of the glacial river must almost 

 certainly have been transverse to the direction of the ice flow, but often 

 we are in doubt as to the direction of ice flow during the very last of the 

 Glacial period. Doubtless many of the deflections then prevalent were 

 never recorded, since the movements took place over land already covered 

 by the ground moraine, and scratches made on rocks then bare of till have 

 usually weathered away. Hence it may often be that these apparent 

 deflections from tine direction of ice flow are not such at all, as we shoitld 

 see could we find the record of the latest glaciation. 



I can assign no physical cause for the formation of subglacial tunnels 

 for long distances in a direction transverse to the flow of the ice, except in 

 regions much broken by crevasses, sucli, for instance, as those near the 

 outer terminal moraines. This seemed likely to afl^ord a crucial test 

 between the subglacial and the superglacial streams, but uncertainties as to 

 the direction of flow of the ice during the very last of the Ice period, and 

 as to the power of a superficial stream to cause an extension of a subglacial 

 tunnel to follow nearly its own course, have intervened. Just as we get in 

 sight of a crucial test it eludes us. 



