SUBMERGENCE PHENOMENA 613 



setts are similar to those of the rocky areas of northern New York and 

 Vermont that have been subjected to immersion (76, page 11). 



JO. ABSENCE OF FOSSILS 



The absence of fossils from the higher horizons of the submerged terri- 

 tory is not sufficient argument against marine submergence. Marine 

 fossils are rarely found in deposits laid close to the glacier margin. The 

 physical conditions which appear to have inhibited life were: the me- 

 chanical effect of coarse and moving detritus, the muddiness of the 

 water, the low temperature, the low and variable salinity, and the lack 

 in the glacial outwash of organic matter required as food. 



The Maps 



The general map of isobases of Post-Glacial uplift, figure 1, is repro- 

 duced from the preceding paper (81), and the local map, figure 2, 

 shows the isobases for southern N"ew England in more detail and with 

 some modification of the earlier map, the latter chiefly in a slight in- 

 crease of the uplift. 



The lines are generalized and regularly spaced, yet express the facts 

 from field study in a surprising degree. It might be supposed that 

 some irregular rise of the land, or crustal warping, would produce 

 variation in the upcurved surface, expressed in irregularity in the 

 isobases. It appears probable that most of the diastrophic movement 

 in the land surface is due to compression and expansion of the earth'.^ 

 mass, and that such great depth is involved that differences in the sur- 

 face lithology would have little or no effect. As the larger topographic 

 features were very old, and isostatic equilibrium had long been estab- 

 lished, the surface relief could have little effect, except as conditioning 

 the depth of ice. 



Future intensive study may relocate the isobases, mth possible recog- 

 nition of some slight irregularity. In the main the map expresses the 

 large truth. It is based on wide field study, not only of the limited 

 area, but of the surrounding territory. 



Emphasis is not laid on great precision of the figures and no effort is 

 made to give figures within multiples of five. There are various sources 

 of errors, as inaccuracies in the old topographic maps; in the railroad 

 elevations; uncertainty in the interpolation between the 20-feet con- 

 tours; errors in the aneroid measurements; and possibly, though not 

 probably, to irregular warping of the land surface. However, with du • 



