22 NEW YORK STATE MUSEUM 



erosion and that the coarse gravel was deposited upon the eroded 

 surface. (The middle layer evidently consists of weathered clays.) 

 Assuming that the upper layers of the clays were originally at the 

 same level here as on the west side of the depression, about 70 feet 

 of clay have been removed by erosion. 



Reserving for a moment the further interpretation of the section 

 we may notice other features of the Round lake depression. On as- 

 cending the hill above the section just described, going toward 

 Malta, the surface material is till up to about 340 feet eleva- 

 tion. Beyond that are the sands of the Malta plain rising to the 

 level of 380 feet. Thus in ascending the hill from the creek we 

 cross successively stratified clays, a deposit of gravel, till, and a 

 thick surface bed of sands. The floor of the depression 

 is largely composed of till but with a broad area of 

 clays along Anthony kill. There is a ridge of till extending 

 from the site of Round Lake village southeasterly across the floor 

 of the basin. South of Round lake this ridge rises to the height of 

 100 feet above the level of the clay area, forming a dome-shaped, 

 boulder-strewn hill. To the west of this ridge there is a low-lying 

 swampy tract the surface materials of which are varied — clay, sand, 

 till and vegetable debris entering into their composition. North of 

 the clay flat along Anthony kill, till is the predominant material of 

 the floor. The slopes surrounding the depression at the higher levels 

 are everywhere sand except where the rock valley of the inlet 

 stream of the lake opens into the depression. 



All of these features become clearly understood by the following 

 interpretations. 



A rock basin occupied the site of the present depression in pre- 

 glacial times. 



With the melting of the ice till was distributed unevenly over the 

 floor and the slopes of this basin. 



Water from the melting ice and from the sources which supplied 

 Lake Albany filled the basin and merged it with that lake. 



Deposits of clay and afterward of sands, made widely in Lake 

 Albany, filled in the basin and for the time being obliterated it. 



When Lake Albany began to subside powerful currents of water 

 entering from the Ballston channel cut into the deposits. 



The erosion of the deposits thus initiated continued pari passu 

 with the subsidence of Lake Albany and resulted in the present 

 topography and the exposures of materials on the slopes and floor 

 of the depression as above described. 



An incident of the last stage was the deposition of eroded and 



