GLACIAL GRAVELS OF COASTAL REGION. 381 



and clays. The difficulty of accounting for the deposition of gravel in the 

 open sea without the formation of a delta is very great, if not insuperable. 

 A very important fact to be noted relates to the size of the gravel 

 deposits at different elevations and distances from the coast. The osars and 

 broad osars become discontinuous at or below the contour of 230 feet, but 

 the longer gravel systems are continuous farther south than the shorter 

 ones. But no matter how large the gravel systems are, they all become 

 discontinuous before reaching the present shore of the sea. Invariably the 

 size of the osars and osar terraces becomes smaller as we go south from the 

 contour of 230 feet, and the intervals between the successive deposits 

 increase. This remark applies to the solid ridges and domes. The marine 

 deltas which here and there appear in the midst of the line of lenticular 

 ridges interrupt the symmetrj'^ of the development, since they are much 

 larger than the ridges and domes situated in the series both north and 

 south of them. But measured among themselves, as a class, the marine 

 deltas are largest near the con- 

 tour of 230 feet and diminish in 

 size southward. This rule can 

 not always be proved — as, for 



instance, in case of the Katahdin F,G.30.-Mariueclayoverl.vinKbaseof osn,-; Hampden. 



system, where the deltas are situated in different drainage basins and it 

 is difficult to compute the average depth of the delta. Apparently the 

 delta west and northwest of Deblois is the largest of the system. It is that 

 which is situated farthest south. But the case is complicated by the fact 

 that the Seboois-Kingman system may have helped -form this delta, and 

 also by the fact that it rises nearer the 230-foot level than the Silsby Plains 

 situated 20 miles northwest. The great development of the glacial sedi- 

 ments not far from the contour of 230 feet is still further aided by several 

 of the larger gravel systems of the Andi'oscoggin Valley which come down 

 to near or a little below that elevation and then end — the Chesterville- 

 Leeds, Canton- Auburn, Peru-Buckfield, and Sumner-Minot systems. 



In most cases the gi'avel systems of all types end before they reach 

 the line of the present coast. The ridges grow shorter and smaller till they 

 are only heaps 10 to 15 feet high, while the intervals between them grow 

 on the average larger. In Western phrase, the gravels ''peter out." The 

 only places where they plainly end in bluffs on the shore are at the north 



