146 H. L. FAIRCHILD PLEISTOCENE GEOLOGY OF NEW YORK STATE 



weak but definite moraine. It is weak because the ice had plastered its 

 load of drift into the drumlins. 



From the relation of the ice-front to the glacial waters and other data, 

 it has been roughly estimated that the thickness of the ice over the mid- 

 dle of the drumlin belt was about 900 feet, or more than 700 feet over 

 the tops of the highest drumlins. 



Marginal: moraines. — The only map published to the present time 

 that shows moraines in detail is that by Tarr in the Watkins Grlen-Cata- 

 tonk Folio (No. 169), which is accompanied by good description. This 

 map, Surficial Geology, covers eight quadrangles of the south-central 

 portion of the State, and includes the upper (southern) ends of the 

 Seneca and Cayuga valleys. Except a few fragmentary moraines in the 

 east and west stretch of the Susquehanna and Chemung valleys, there 

 are almost no moraines south of the divide, as already noted in this writ- 

 ing. The lines of drift massing show decided lobation of the ice in the 

 valleys north of the divide and conformity to the land surface. The 

 plastic ice was here flowing on its own deposits and had no erosive power. 

 Probably the only moraines in the State that can properly be called 

 "lateral" lie in these valleys. 



In the west half of the State the heavier or more conspicuous morainic 

 belts have been approximately located, though little precise mapping has 

 been attempted. The most recent and definite is by Leverett, 9 and a 

 sketch cap, figure 11, page 15, in the Folio 169. These morainic belts 

 clearly show the larger lobation of the waning ice-sheet in the Ontario 

 and Erie basins. 



In the east half of the State the moraines have been located in only 

 few places, excepting the terminal moraine. In the Hudson and Cham- 

 plain Valley Woodworth has recognized some fragments and ice contacts. 

 This difference in moraine development between the two parts of the 

 State is due to the difference in the gross topography. A glance at the 

 map shows that on the Hudson-Champlain meridian the distance cov- 

 ered by the receding ice-front is greater than in the Ontario Basin, so 

 spreading the drift over more area. The rocks in the east part of the 

 State are more resistant to erosion, due to kind and structure. The 

 Hudson ice-lobe and its successor in the Champlain Valley were always 

 faced by ocean waters, and the terminal drift in the bottom section of the 

 great valley was mostly scattered and buried under the water deposits. 

 On the high grounds east and west of the marine inlet the surfaces are 

 so rough, or even mountainous, that the moraine deposits lack continuity 



U. S. Geological Survey, Monograph XLI, 1902. 



