ORIGIN OF GLACIAL GEAVEL COMPLEX. 459 



the highest level of the sea and for 20 miles or more, as happens in south- 

 western Maine, the gravel was undoubtedly being deposited in stream chan- 

 nels in the ice at a distance back from the front at the same time the deltas 

 were forming. While the delta was forming the ice would be retreating, 

 and the retreat of the ice would uncover the ice-channel ridges, to be at 

 once covered by gravels poured out by the glacial streams which now 

 flowed into the sea at some point northward. In these cases I infer that 

 ice-channel and frontal ridges are both represented in this class of marine 

 deltas. The case would be still more complicated if the delta began as a 

 glacial lake or broad channel deposit. The history of each delta is to be 

 deduced from the local conditions, and probably in the various delta com- 

 plexes we have every variety and combination of ice-channel sedimenta- 

 tion, with that which takes place in bodies of water in front of the ice. 



RETICULATED KIDGES AT THE PROXIMAL ENDS OP THE GLACIAL LACUSTRINE 



DELTAS. 



Elsewhere are described what appear to be lake deltas at East Brown- 

 tield, in North Shapleigh, in Unity and Thorndike, in Dixmont, in Newburg, 

 and in other places. Two or three are possibly below the highest level of 

 the sea and may be marine, or partly marine. All are north of hills, where 

 fringing lakes would be formed during- the retreat of the ice down the 

 northern slopes. I see no points bearing on their origin other than those 

 applying to the marine deltas. 



RETICULATED RIDGES AS A PART OF GLACIAL LACUSTRINE MASSIVES. 



These are the massive or solid mounds and mesas of coarse' sedi- 

 ments, showing little horizontal assortment, which I assume to have been 

 deposited in gradually enlarging lakes within the ice. They sometimes 

 contain hollows or kettleholes and basins, inclosed by broad, flattish-topped 

 ridges or plains. ' Some of the basins may have formed where the gravel 

 was deposited over masses of ice or around ice islands. If deposited on 

 the ice, I infer that the gravel would lose its stratification during the melt- 

 ing of the ice. More often probably the basins in this class of gravels are 

 unfilled portions of the lake, left where broad reticulating ridges failed to 

 coalesce completely. This sort of sedimentation would result from the 

 stream pouring into the lake from different points, either simultaneously 

 or in succession. 



