ISOBASES 239 



Professor Salisbury says (97, page 203) : "On the whole, the evidence 

 seems to favor the conclusion that the northwestern part of the State 

 (New Jersey) was covered by standing water to the depth of 100 feet or 

 more after the ice retreated, though this conclusion can not be regarded 

 as beyond question. If this be correct, the area has risen a corresponding- 

 amount since the ice melted." And F. J. H. Merrill gives the amount 

 of uplift at Few York City as 80 feet, and at Peekskill as 120 feet (63, 

 page 105), which accords with the map altitudes. In giving Croton 

 Point as 100 feet, which is about 15 feet too low to harmonize with his 

 other altitudes, he only made the common error of accepting the broad, 

 conspicuous delta plains as the summit level. 



The zero isobase is drawn parallel with the 100-feet line so as to touch 

 Ashtabula, Ohio, which point is given by Leverett as the locality where 

 the Maumee and Whittlesey beaches lose horizontality (100, pages 755- 

 756). This position for the zero line accords precisely with Goldthwait's 

 limit of horizontality of the early beaches in the Michigan Valley (108, 

 page 465). These locations of the zero and 100-feet isobases, based on 

 well-determined beach altitudes, gives the increased spacing required by 

 theory. 



In the Whittlesey and Warren shorelines we have yet other checks, on 

 higher altitudes farther north. Using Leverett's figures as far as Marilla, 

 we find that the total uplift at that locality is 164 feet. As the isobases 

 lie on the map, Marilla is estimated as between 162 and 165 feet. Pond 

 triangulation station, 8 miles northwest of Batavia, is the highest point 

 on the Warren beach, with altitude 887 feet (118, page 77). This is 32 

 feet higher than the same beach on the Marilla isobase, which gives us 

 196 feet for the uplift at Pond; and the point is just over the 200-feet 

 isobase. When the several variable factors are considered, the corre- 

 spondence of the isobases on the map with the field data is remarkably 

 close. 



The only question which can be raised as to the validity of the isobases 

 on the Hudson-Champlain meridian is whether they indicate the whole 

 amount of Pleistocene uplift. They have been determined by study of 

 the abundant shore phenomena practically continuous along both sides of 

 the Hudson-Champlain and Connecticut valleys, and therefore they can 

 not represent too great depression and uplift. The objection to the sea- 

 level character of the waters has been on account of the deep submergence 

 which the beaches imply. 



If the isobases do not represent the total land movement, it must be 

 because some rising occurred in areas covered by the glacier, so that the 



