140 H. L. FAIECHILD PLEISTOCENE GEOLOGY OF NETV YORK STATE 



South of the divide morainal drift is almost entirely lacking in the 

 south-leading valleys and only scantily represented in the larger east and 

 west Susquehanna and Chemung valleys. Tarr says : 



"On the upland, south of the area of the recessional moraines, little moraine 

 material is found and no definite system has been worked out. 



"The complex of moraines in the northern part of the Watkins Glen quad- 

 rangle aDd the northwestern part of the Catatonk quadrangle, contrasted with 

 the general absence of moraines in the southern half of the area, forms one of 

 the most striking features of the Quaternary geology'* (page .17). 



The heavy morainal drift in the valleys north of the divide was not 

 derived from erosion of those valleys, but was the accumulated rock rub- 

 bish acquired by the lower part of the ice-sheet during its entire journey 

 across the State. When the ice was thick enough to override the divide 

 and flow south, it was the superficial, drift-free ice that passed across, 

 while the lower, drift-loaded and relatively stagnant ice reposed in the 

 Ontario Basin and its valleys, serving as the bridge, that was overriden 

 by the clearer and more plastic superficial layers. In evidence of this is 

 the relative absence of drift south of the divide and the almost entire 

 absence of crystalline rocks or far-traveled material. Quoting Tarr : 



"In the uplands south of the recessional moraines foreign fragments are 

 much more rare, and in some parts of the uplands a careful search is required 

 to find even a small pebble of crystalline rock, while boulders are practically 

 absent" (page 16). 



To whatever extent the ice in the margin of the snowfield was pro- 

 duced by the centrifugal, anticyclonic winds from the interior of the ice- 

 cap, as suggested by Hobbs from study of the existing continental gla- 

 ciers, 6 it also favored lack of drift in the periphery of the ice-body. With 

 the waning and thinning of the ice-cap the drift-loaded lower ice was 

 finally uncovered so as to constitute the marginal belt, and was then sub- 

 jected to thrust or push from the thicker body on the north. At this 

 stage the heavy moraine deposits were made in the valleys, producing 

 the present drainage divide, and the lobations of the ice-front built the 

 concentric lateral terminal ridges north of the divide. At a later stage 

 of the waning, when the required factors were properly combined and 

 balanced, the drumlins were constructed on the lowlands, northward. 



Many facts are cited by Tarr showing the impotency of the latest ice- 

 sheet, and he finally admitted that the "Wisconsin ice-sheet failed to 

 notablv modify the topography in the sweater part of this area" (page 

 16). 



6 Characteristics of existing glaciers, 1911. 



