LAKE ESCARPMENT MORAINES. 667 



knolls abound. Grravel knolls are more conspicuous in the valley-like 

 depressions than on the ridges, both in the district north from Cattaraugus 

 Creek and that west from it in Chautauqua County, N. Y. 



The interlobate moraine carries a large number of gravel knolls, and 

 the till knolls contain a large amount of coarse material. The depressions 

 among the knolls have, on the whole, a coarser drift than is usually found 

 in the portion west of the interlobate, where a compact till predominates. 



The portion of this morainic system between the interlobe and the 

 Genesee River has about the same structure as the interlobe, there being 

 a large number of gravel knolls and a rather stony drift in the till knolls. 



Surface bowlders are common all along the morainic system, but are 

 especially abundant in the New York portion. They are largely granitic 

 rocks, though in many places Canadian crystallines are represented. 



Parts of this morainic system have been classed with the beaches by 

 early writers.-^ This confusion appears to have arisen mainly from the 

 imperfect knowledge of the phases of structure which a moraine may pre- 

 sent, especially the stony phase, though in one of the instances above cited 

 a ridge of clayey till is called a beach. In Read's "Profile section from 

 Lake Erie to Glrand River," ^ the southernmost of the four ridges there 

 shown is the Painesville moraine and is described as a ricige of bowlder 

 clay. The beaches are narrow ridges only a few rods wide, while the 

 moraine has a width of one-half mile or more. The beaches are composed 

 of assorted material, the moraine pf till, with occasional developments of 

 gravelly knolls In places in Ashtabula County the moraine and beach are 

 so closely associated that beach sand appears on the moraine, but through 

 much of its course in Ashtabula County, as well as elsewhere, the moraine 

 is free from beach deposits and from evidences of wave action. The 

 following description by Read, taken from the report on Ashtabula County,^ 

 will make it evident that a glacial ridge rather than beach is desci'ibed: 



The old "lake ridges" and terraces are well defined in the county, and railroad 

 excavations haveafi'orded unusual facilities for studying their character. The outer 

 or southern ridge, where exposed by railroad cuts, is shown to be a ridge or wall of 

 compact unstratified clay, composed largely of the local rocks, but with many frag- 



'I. C. Wl?ite: Second Geol. Survey Pennsylvania, Bept. Q*, pp. 38,39. M. C. Read: Geology of 

 Ohio, Vol. I, 1873, pp. 488^90, 516-518; Vol. II, 1875, pp. 60-63. 

 ' Geology of Ohio, Vol. I, p. 518. 

 ' Geology of Ohio, Vol. I, p. 488. 



