LATE GLACIAL CONDITIONS 9 



ice the region south of the Baltic stood higher than now, while 

 Fenno-Scandia was submerged. The evidence collected is 

 believed to indicate that the magma was pressed ouc from under 

 the center of the ice sheet, causing the peripheral regions to rise. 

 As the ice melted and the pressure decreased, the magma regained 

 its lost ground, and so the receding ice edge was followed by the 

 crest of a wave of elevation. When the crest passed northward, 

 the peripheral region sank until equilibrium was regained. 

 Whether the sinking of the southern New England region was 

 interrupted by oscillations or not is unknown. 



Physiographic evidences for an elevation of the lower Hudson 

 district in late glacial time were presented long ago by Wood- 

 worth (1905a, p. 229; see also Barrell, 1915, p. 15). The opinion, 

 advanced especially by Fair child (191 4, 191 9), that southern 

 New England and New York were submerged at this time does 

 not seem to be supported by any facts. 



The district south of Boston, when uncovered, seems to have 

 had the same elevation as now, while the land north of it was 

 depressed beneath the sea and with increasing amount towards 

 the northwest (PI. VI). 



Formation of Lakes at Ice Front; Their Sediments 

 the Records Here Studied 



Because of this northward inclination of the land, chains of 

 long narrow lakes were ponded off the receding ice front. By 

 some geologists these have been regarded as bays of the sea. 

 In recent years Goldthwait has undertaken to revise the water 

 levels in the Connecticut and Merrimac Valleys by detailed 

 study. The exact position of the extinct water planes is not yet 

 known, and so only the general outlines of the lakes after Lough- 

 lin (1905), Emerson (1898), and C. H. Hitchcock (1878) are 

 shown in Figures 5-13. 



Glacial rivers loaded with material discharged into the lakes, 

 and each year a varve of clay or silt was deposited all over the 

 lake bottom. The deposition, if undisturbed, proceeded until 



