REPORT OF THE DIRECTOR I915 IO9 



those in the micidle and southern section is from 180 to 200 feet, 

 but there are still lower ones in the south. 



The sands and clays were laid down in standing water and their 

 deposition dates back to late Pleistocene time when the Hudson, 

 instead of flowing freely to the sea as now, was held back or im- 

 ponded so that its waters reached the higher levels' marked by the 

 terraces. The sediment swept into this temporary lake by the 

 Mohawk and other tributaries was deposited layer upon layer until 

 the accumulations attained an elevation of 400 feet or more above 

 the old river bottom and extended from side to side of the valley 

 depression. With the later lowering of the outlet the waters were 

 drained off and the river began cutting down a channel through the 

 soft beds which it now occupies. 



The clays and sands retain their original stratified , arrangement 

 for the most part; the former especially show a division into 

 longitudinal layers or seams just as they were first deposited. 



The clays occur mostly in the lower and the sands in the upper 

 part of the series. The latter were laid down in the closing stages 

 of the history of Lake Alban}^, as the flooded valley is called, and 

 originally formed a mantle over the whole district. It is these sur- 

 face sands that are of present interest. 



Distribution and Occurrence of the Sand 



At the present time the sand deposits are by no means continuous 

 over the whole district. Lying at the surface they have been sub- 

 jected to erosional influences which over some areas have effected 

 their complete removal. In general, they are not very thick, 15 or 

 20 feet being about the maximum, except w"here the)^ have been 

 heaped up in ridges and dunes by the work of the winds. The 

 action of the wind has a prominent part in the present arrangement 

 and distribution of the sands, and they are still being shifted about 

 wherever they are not anchored by a mantle of soil and vegetation. 

 The area covered by the old Mohawk delta contains tracts occupied 

 by live dunes that are in course of continuous change as to form 

 and position. Frequently the topography bears evidences of similar 

 wind work, although the surface may have been protected from it 

 for a long time. 



In consequence of this working over by the winds the sand now 

 occupies no definite position in the series, but is distributed over 

 the surface from near sea level to several hundred feet above. Its 

 contact with the clays below may be seen in places to be quite 



