80 



NEW YORK STATE MUSEUM 



onal valleys on the one hand like that of the Hudson and broad 

 njdands or sea border jdalns, on Hie olher snch as occur over cen- 

 tral and southeastern Massachusetts. Here we are solely con- 

 cerned with a long, well defined meridional valley. 



As the ice front retreats northward there is found evidence of 

 its having halted from time to time at certain places long enough 

 to build moraines of dumped and shoved material on the one hand, 

 and to allow the construction, from the outwash of sands and 

 gravels, of deposits of these materials in the form of i)lains, cones 

 and deltas more or less sharply marked on their northern or ice- 

 ward aspect by evidence of deposition against or in the presence 

 of masses of melting ice. The ice melting out back of such accu- 

 mulations, either moraines on the one hand or outwash plains on 



^9.0.!^.''- 





yjAizR 



Yin. :i. Siicccssi on of glacial deposits (lurinj>- letroat. Theoretic distribution of glacial 

 deposits from north to soutii in New York and New England : yl=rsta}re in which a moraine 

 has been formed and is eonf routed by an overwash plain : ii=overwash and outwash plains; 

 C=a. later moral nal stage with outwash sands. 



the other, may have left but a veneer of till or gi-avel over the gla- 

 ciated bed rock. At an indefinite distance to the northward other 

 frontal accumulations will aj)pear marking the next stage in the 

 retreat. 



In the case of these deposits the coarsest detritus of glacial 

 origin will appear next the ice front of the time in the form of till 

 or of coarse gravels and sand; farther away in the direction of 

 the flowing waters finer sands Avill ai)pear and still farther away 

 tlic clnys w liicli i-(mii;i iiied for a lime in susi)ension. The suc- 

 cession of deposits will appear as in the above diagram [fig. 3.] 



Tf the deltas ai-e built in standing water their outer lobate mar- 

 gins will indlcMic jlic aj)j)roximate hight of the water plane of the 

 time, 1m' il sea level or lake level. If building takes place on an 

 area fn.m which the waters escape to the sea without ponding. 



