GLACIAL GEOLOGY OF THE SARATOGA QUADRANGLE 1 5 



clearly shows the local origin of much of the rock debris. In the 

 mountainous areas and in the northern portion of the central basin 

 the till is characterized by a relatively large amount of sand enter- 

 ing into its composition. In these regions the soils, lacking the 

 clay constituent, are of loose texture and are poorly adapted for 

 agriculture. Boulders and cobbles of gneissic and other crystalline 

 rocks are abundant. These features of the till are clearly to be 

 connected with the source of the materials from the Precambric 

 rocks to the north. 



In the southern portion of the central basin where the under- 

 lying rock is limestone and in the southwestern portion of the 

 quadrangle where the bedrock is shale and shaly sandstone, the 

 clay element in the till is in larger proportion and the lands are 

 capable of productive cultivation. 



The thickness of the till varies widely in different localities, 

 ranging from zero, where bare rock surfaces occur, to more than 

 200 feet, as measured by the height of the highest drumlins. In the 

 eastern highlands region the till is for the most part thin; thus 

 along the roads running eastward from Greenfield Center to Kings 

 Station there are numerous exposures of bare rocks. In many 

 places, especially along the more northerly of the two roads, the 

 till is of such slight thickness as to have been washed away from 

 the roadside gutters. 



In the southern portion of the central basin and extending south- 

 westward across the quadrangle there is a heavy mantle of till, 

 showing in places a thickness of 200 feet. A natural section of the 

 till is afforded near Rock City Falls where Kayaderosseras creek 

 has cut through the formation to bedrock. The mass of till (which 

 forms a drumlin in its upper portion) south of the creek shows an 

 elevation of 240 feet above bedrock. 



This marked difference in respect to the thickness of the mantle 

 of till, as between the two regions just referred to, is evidently due 

 to the influence of topography in determining the deposition of 

 debris carried by the ice sheet. As the ice moved across the high- 

 lands it scoured off the preexisting soils and rock fragments and at 

 the same time broke off and to some extent ground down project- 

 ing ridges and ledges of rock. The materials thus gathered were 

 deposited by the advancing ice sheet in the old valley, the course of 

 which lay across the path of ice movement. The effect was to re- 

 duce the general relief of the older topography, the western slope of 

 the highlands having been somewhat smoothed down, while the old 



