ELISHA MITCHELL SCIENTIFIC SOCIETY. 47 



ied by a spreading" out of its mass on all sides so that 

 it extended southward far into temperate lattitudes, 

 reaching- at its g-reatest extension the middle courses 

 of the Mississippi River. On the Atlantic coast of 

 New Kngland the g-lacial covering spread into the sea 

 and jDi'obably floated off as icebergs. As a result of 

 the abrasion and transport of rock material by the ice, 

 the glacial field is covered with deposits of irregular 

 distribution and possessing the peculiar characters by 

 which they are readily distinguished from ordinary 

 aqueous sediments. During the formation of some of 

 these glacial heaps, the land along the North Atlantic 

 coast must have stood somewhat higher than at present. 

 Some of these deposits, which were evidently made 

 upon the land, now lie as small wasting islands off the 

 present shores. Indeed it has been claimed that the 

 central part of the glacial field must have stood much 

 higher at the beginning of the glacial period than now, 

 the difference amounting to thousands of feet in the 

 region just south of Hudson's ba3% which was sup- 

 posed to have been the glacial centre. This has been 

 supposed a necessary condition to account for the accu- 

 mulations of snow and ice in such enormous quantities, 

 and its descent into lower latitudes. There is 

 evidence of such a condition in Europe in the horded 

 Scandinavian coast, as has been pointed out by Dana, 

 and the submerged valleys extending out from the 

 Hudson and other rivers may be cited as an American 

 evidence of a similar sort. But we have much clearer 

 evidence of submcrg-ence during a later part of the 

 glacial period, v/hich amounted to onl}^ a few feet at 

 New York City but increased northward, — reaching 

 200 to 225 feet off the coast of Maine, 500 to 600 feet 

 at Montreal and 1000 feet on the coast of Labrador. 



