454 GLACIAL GRAVELS OF MAINE. 



ice into the still water would form a ridge on each side of it, and these 

 lateral ridges would be connected by a cross ridge at a distance from the 

 mouth of the stream depending on the size and velocity of the stream, the 

 depth of still water, the size of the transported stones, etc. This transverse 

 ridge is due largely to the whirl of the water where the swift water enters 

 the still water. If a number of parallel streams of different sizes entered a 

 body of still water, the transverse ridges would be formed at different dis- 

 tances from the mouths of the streams. The result woiild be the same if 

 a stream abandoned its former channel for a new one. As the ice melted 

 and the ice front receded, new transverse ridges would be formed from time 

 to time. Perhaps it would describe the phenomena better to state that the 

 two lateral ridges bend their courses so that they unite, rather than to use the 

 term "cross ridge," as if this ridge were distinct from the lateral ridges, for 

 it is only a deflection of them, formed in a curve on the outside of the whirl 

 where the swift water is checked and set to whirling by the mutual action of 

 the still and the rapid water. 



When small glacial streams build up each its own delta ridge beneath 

 still water, the radiating ridges may approach one another and thus inclose 

 basins. 



2. By glacial streams in ice channels beneath the level of compara- 

 tively still water. This would more often happen in case of subglacial 

 streams. The method would be substantially the same as when basins are 

 formed above the sea. 



3. In the lee of a broad obstruction situated in the midst of a flowing 

 stream. Bars of gravel extend from each side of the obstruction, which 

 curve convergently so as to leave a crescentic basin between the coalescent 

 bars and the obstruction. I have seen such basins in the lee of small islands 

 in the salt-water fiords and inside "rivers" along the coast. In case of 

 glacial rivers entering lakes or the sea, this may have been an important 

 condition for the forming of basins. 



4. By the unequal filling of subaqueous channels. The shifting bars of 

 the Western rivers must often leave portions of partly filled channels as deep 

 pools, which would become kettleholes or other-shaped basins if raised 

 above water. The terraces of valley drift are in general very level on the 

 top, showing that they were deposited under very different conditions from 

 those of the reticulated ridges on the alluvial plain of the Androscoggin 



