SYSTEMS OF DISCONTmUOUS OSARS. 395 



CAUSES OF NONCONTINUOUS SEDIMENTATION WITHIN ICE CHANNELS. 



The nature of the phenomena here referred to can best be understood 

 by consultmg the descriptions of the discontinuous and continuous osars, 

 also of the osar terraces. They are briefly set forth as follows: If we start 

 from a point 30 or 40 miles from the coast and g-o southward, we find the 

 gravels becoming more and more discontinuous (and correspondingly 

 smaller in size), and almost all the systems end a short distance from the 

 shore and at only a few feet above tide water. That gravel systems of 

 varying' lengths and having very different topographical relations should 

 terminate over the whole coast at almost the same level is a remarkable 

 fact and apparently associated with the feature of noncontinuity. 



Omitting' from present consideration the deltas which were deposited 

 in the sea or in lakes sufficiently large, relative to the inflowing glacial 

 river, to permit a horizontal classification of sediments from coarse at the 

 proximal to the finest clay and rock flour at the distal end, we confine the 

 inquiry to sediments deposited in ice-bordered channels or basins, under 

 such conditions that the finest of the glacial d(jbris was carried away by 

 the glacial i-ivers and only the coarser left. We premise that each of the 

 discontinuous osar systems, as well as the discontinuous portions of the 

 osars, was deposited by a single glacial river. The question then resolves 

 itself into this : How can a glacial river systematically deposit sediments at 

 intervals in its channel and the intervals increase as the size of the gravel 

 deposits decreases! 



Noncontinuous sedimentation by a single glacial river mig-ht be accom- 

 plished in three ways : First, the river might be depositing sediments in two 

 or more separate parts of its channel simultaneously, the intermediate por- 

 tions of the channel being at the same time areas of erosion and transpor- 

 tation; second, sedimentation might proceed by stages, the separated 

 deposits being made one after the other, each one being finished before the 

 next of the series was begun; third, both these methods might be in 

 operation simultaneously in different parts of the same glacial river. 



Again, part of the physical agencies that lead to noncontinuous sedi- 

 mentation may be operative only when the tunnels of the subglacial 

 streams open beneath the sea or other body of water, and others may 

 depend wholly on conditions originating within the glacier itself or on other 



