OEIGEX OP GLACIAL GRAVEL COMPLEX. 455 



River above Gileacl or the channel of such a river as the Platte, if it could 

 be drained dry. 



5. Where large quantities of sediment are being carried downward by 

 a rapid stream, transverse bars naturally form across the stream, in which 

 the grains or stones that are behind pass to the front, one after another, like 

 the grains in a dune of blowing sand or in a ripple-mark. Bars of this 

 kind, so far as I have observed them, are not large enough to be consid- 

 ered the correlatives of the large transverse ridges so common among the 

 plains of reticulated kames. 



The influence of tides in causing the formation of ridges and hollows 

 by checking the glacial streams has not been formally included in this 

 list, since it is doubtful how far tidal influence was felt by them. Yet the 

 tides may in certain cases have had some efPect of this kind. The tides 

 would help to a horizontal stratification of the finer sediments. 



In 1878 I suggested in the American Naturalist^ that certain ridges 

 that project like tongues from the side of the alluvial plain of the Andros- 

 coggin near the line between New Hampshire and Maine were due to the 

 overflow of the river in time of flood into a lateral valley containing a lake 

 during high water. It is still a question whether there is not a particular 

 size of sediment fragments which, with a proper depth and velocity of 

 stream, will tend to form an uneven bed covered by shifting bars and hol- 

 lows, while if the fragments become smaller than this the stream will fill 

 up the inequalities of its own production and flow over a level plain. The 

 drift of the upper Androscoggin Valley is perhaps the key to this problem, 

 if one milj knew how to use the key. 



ORIGIN OF THE GLACIAL GRAVEL COMPLEX AND ITS RELATION TO MARINE 

 AND LACUSTRAL DELTAS. - 



PLEXUS SITUATED AT ONE END OP A MARINE GLACIAL DELTA. 



Here there is a gradual horizontal passage of sediments from coarse at 

 one end of the delta to fine sand and finally clay, all having the same level 

 as the adjacent beds. At the end where the coarser sediment is, the plain 



' Note on the Androscoggin glacier, Am. Naturalist, vol. 14, pp. 299-302, 1880. 



- The theory that the kames were deposited in the sea was enunciated in a paper by Prof. N. S. 

 Shaler, in Proc. Boston See. Nat. Hist., vol. 23, pp. 36-44, and to Professor Shaler.is due the credit 

 of first publication. My own views were worked out independently by a study of the ridges formed 

 below dams, as elsewhere described. 



