234 H. L. FALRCHILD PLEISTOCENE MARINE SUBMERGENCE 



charts plate 11, for both the Connecticut and the Hudson-Champlain val- 

 leys. The form of this chart is borrowed from Woodworth's Plate 28, 

 in Bulletin 84, N'ew York State Museum. For the Connecticut Valley 

 the theoretic or datum plane is based on Emerson's figures, 288 feet on 

 the south line of Massachusetts and 400 feet on the north boundary. So 

 far as observation has reached, the summit-level phenomena throughout 

 the valley agree remarkably close with this hypothetic plane. 



The line representing the Hudson Valley plane is drawn coincident 

 with numerous summit features. 



It is not supposed that the actual uplifted and tilted marine plane is a 

 perfectly straight surface, but such irregularities or warping as exists 

 would probably not be evident in the condensed chart. The area of New 

 England and New York probably was not uplifted as a rigid mass, yet 

 any wavelike uplift following the waning ice-body might in its final result 

 approach the regularity of a plane. The altitude variations of the shore- 

 line features of the summit level will usually not vary from the indicated 

 plane more than the natural variation in height of such phenomena com- 

 bined with the errors of measurement that refer to the 20-feet contours 

 of the old topographic sheets. 



Shoreline features or phenomena of standing water found much above 

 this datum plane will belong to glacial waters held up by the ice-front. 

 When evidences of standing water are found much below this plane, 

 search should be carefully made for higher features; but it should be 

 emphasized that local absence of shoreline features is ver}^ common, and 

 such negation has no weight against positive occurrence of the phenomena 

 at other places. Long stretches of shoreline may yield very faint evi- 

 dence or even none at all. 



The slope or gradient of the marine plane in the Connecticut Valley is 

 2.30 feet per mile. In the Hudson Valley it is 2.23 feet per mile. This 

 close correspondence is not closer than should be expected. But in the 

 Connecticut Valley the plane lies about 50 feet higher than in the Hud- 

 son. This throws the isobases about 20 degrees north of west by 20 de<- 

 grees south of east, as depicted in the map, plate 11. 



In the northern part of the valleys the marine plane apparently has 

 a steeper gradient, or, in other words, the original plane is warped upward 

 at an increasing rate in the Champlain Valley and probably in the New 

 Hampshire portion of the Connecticut Valley. In the Champlain Valley 

 heSiYj beaches which can not be referred to glacial lakes lie much above 

 our datum plane, which at the international boundary is about 695 feet, 

 while strong cobble bars occur two miles south at 730 feet. 



