EETIOULATED BSKERS OR KAMES. 453 



FORMATION OF KETTLEHOLES AND OTHER BASINS INCLOSED BY RIDGES 

 OR BY PLAINS OF AQUEOUS SEDIMENTS. 



I. Such hollows or basins may be formed above sea level. 



1. In the channels of glacial streams either above or beneath the ice. 

 This could happen if the streams branched like rivers at their deltas and 

 subsequently came together again, or became connected by cross channels, 

 thus inclosing islands of ice or covering the ice to an unequal depth with 

 sediment. 



2. In case glacial sediments are deposited on the ice and in process of 

 the unequal melting part of the sediment slides one way and part another, 

 or settles in channels of streams. 



3. In the process of delta formation where a number of streams are 

 each building up its own ridge. These streams as they radiate outward 

 will here and there meet or approach one another and their respective ridges 

 will inclose basins. 



4. By unequal fluviatile erosion of previously deposited sediments, 

 such as the deep pools in the beds of streams at the base of rapids or 

 waterfalls. 



5. By subterranean waters in the form of boiling springs. As the 

 waters boil upward they carry off the finer matters of the soil in suspen- 

 sion, and even the matter contained in solution may in time come to have 

 geological importance. In some cases small lake basins may have been 

 formed in this way, such as those near Fryeburg and in the upper Kenne- 

 bec Valley. 



6. By the unequal filling of previously existing channels. The half- 

 moon lakes of the delta of the Mississippi River are instances of this class, 

 and perhaps some of the small lakelets of the alluvial plain of the Kennebec 

 River between the Forks and Embdeu have the same origin. 



7. By ice dams. Before ice gorges give way streams sometimes shoot 

 out tlirough them with sufficient velocity to erode deep holes in the valley 

 alluvium. During the flood which accompanies the breaking of the dam, 

 sediments are sometimes deposited over heaps of ice, and the subsequent 

 melting of the ice blocks leaves a hollow where the thickest ice was. 



II. Such hollows or basins may be formed beneath relatively still water. 



1. By glacial streams flowing into a lake or the sea. Judging from 



the ridges formed below the dam at Kingman, each stream issuing from the 



