OEIGIIs^ OF LAEGEE COMPLEXES. 463 



reticulated ridges, and wlien the latter is jjresent the reticulations are noi 

 so complex as in broad A^alleys or on level plains. The problem of the 

 reticulated kames is, then, closely related to that of the broad osar. In 

 the one case a single channel became very much enlarged and a continuous 

 plain of rather horizontally stratified gravel was deposited over the bottom 

 of the whole broad channel. In the other case the sediment took the form 

 of a series of two-sided ridges, more or less confluent by their bases or by 

 cross ridges. And there are in a few cases transition forms between the 

 two types, as of a terrace or plain having a wavy surface. Furthermore, 

 the same glacial river could in different parts of its coui'se deposit both 

 these forms. We must infer, then, that no special amount of water, or of 

 increase or decrease in quantity of flow, was needed. The process depended 

 not upon the stream so much as upon the ice and the other conditions of 

 sedimentation. These conditions are so numerous that it can with some 

 coirfidence be affirmed that the details of the process would vary in different 

 localities. 



ORIGIN OF THE LARGER COMPLEXES. 



The general process by which the larger plains or complexes of reticu- 

 lated ridges Avere formed appears to be about as follows: 



North of these plains are regions of steep average southward slope. 

 The rapid streams (mostly subglacial in southwestern Maine) brought down 

 great quantities of sediment from the north. As they reached the more 

 level country their velocity became less and the coarser sediment was 

 dropped. In the case of the broad osar channel the deposit of sediment 

 did not proceed faster than the lateral enlargement of the channel and no 

 new channels were formed. A broad, rather leA^el and continuous plain 

 was deposited across the whole of this channel, which was often as broad as 

 the plexus of reticulated kames adjacent. If the water could flow into and 

 through this broad channel, producing a level plain, not an uneven plexus 

 of ridges, how can we admit that the reticulated ridges were deposited in a 

 body of open water as broad as the osar channel"? The osar-plain or ter- 

 race, it seems to me, is the answer to our questions as to what would happen 

 in a single, gradually enlarging broad channel — not a jumble of ridges, but 

 a rather horizontally stratified plain. The evidence here distinctly favors 

 the hypothesis that the ridges of the complexes under discussion are not 



