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NEW YORK STATE MUSEUM 



what at first sight on the basis of long familiarity with glacial 

 drift in other districts was taken to be unaltered glacial till 

 was ascertained to be till partly modified by the action of 

 waves or currents. Thus near Norwood, on the west of this 

 field, marine shells occur at the depth of over 2 feet in what at 

 the surface has all the appearance of glacial till, but which in 

 section shows that it must be regarded as a rubbly layer worked 

 over without distinct stratification or even rounding of the con- 

 stituent rock particles. Usually the action of the sea on these 

 stony tills has been to leave the surface of the deposit strewn 

 with many small blocks of rock, which appear to have accumu- 

 lated on the surface as the result of the washing away to lower 

 grounds of the finer sands and clayey particles of the superficial 

 layer in which the stones were originally embedded. The larger 

 glacial boulders are seldom moved far and often project from the 

 soil as in the case of ordinary till areas. 



The area mapped as " Undifferentiated glacial deposits super- 

 ficially worked over by waves and currents" is of the above 

 described character. Beach lines, and bars of wave-heaped rub- 

 ble are common in the district as shown on the map. This belt 

 rises to a somewhat higher elevation on the southern border of 

 the area than it does on the north. 



Lying above this wave-modified district there are in the north- 

 western part of the area very similar deposits only less distinctly 

 reworked except along certain ancient water levels. The distinc- 

 tion between the two areas is difficult to make and there are 

 large areas in both fields which I am sure are identical in topog- 

 raphy, in composition of the drift, and in structure; yet one 

 distinctly gets the impression in passing from the low grounds 

 to the upland portion of the district on going above an elevation 

 of from 450 to 500 feet, that he is passing from a zone of largely 

 water-laid materials to a region of till. The demarcation in 

 the field between these two areas of more or less modified deposits 

 is usually very vague. I have drawn it on the map at about 

 500 feet in elevation in the northern part of the map because 

 above that line the chief characteristic of the lower belt of mater- 

 ials — the presence of beaches — is usually wanting. 



