360 THE ICE AGE IN NORTH AMERICA. 



them but a short time ; while others, whose bottom is below 

 the general surrounding water-level, or whose rims chance 

 to be of more compact material, retain a small amount of 

 water during the most of the season, or throughout the 

 entire year. In innumerable cases peat has accumulated in 

 the bottom of these, and filled up a considerable portion of 

 the lower part of the cone-shaped depression. It is thus that 

 nearly all the peat-bogs of New England and the Northwest 

 have originated. In numerous cases the peat forms a rim 

 about the edge at the water-level, while in the deeper por- 

 tion the surface of the clear water looks up from the shad- 

 ows, or reflects the sunshine like the pupil of a gigantic eye. 

 In respect to these glacial lakes partially surrounded by 

 accumulations of peat, one almost uniformly finds local tra- 

 ditions that they are without bottom, or at least that no one 

 has been able to find it. The fact is, however, that they are 

 none of them of great depth ; but the soft ooze of muck and 

 mud which accumulates at the bottom renders sounding 

 impracticable, and thus originates the illusion of unfathom- 

 able depths. 



The lakes and bogs of Ireland present familiar examples 

 of this class of glacial in closures ; while in this country one 

 can not easily run amiss of them, either in New England or 

 the Northwest. The southeastern portion of Massachusetts 

 abounds in them in special degree. As before remarked, 

 Plymouth county is little less than a ganglion of such gla- 

 cial lakes with their inclosing deposits — Plymouth township 

 alone being reputed to have three hundred and sixty. They 

 appear all along the line of the terminal moraine, often cap- 

 ping its very summit in the western portion of Long Island, 

 even within the limits of the city of Brooklyn. 



As shown in a previous chapter,* the Elizabeth Islands 

 consist of a network of deposits surrounding such depres- 

 sions ; but in this case, as frequently elsewhere, the rims are 

 of such coarse material that most of the depressions are dry. 



* See p. 205. 



