GEOLOGY OF THE PORT LEYDEN QUADRANGLE 53 



tliin and after the formation of the kames and withdrawal of the 

 ice edge, the delta sands were deposited around them but not with 

 sufficient depth to cover them. 



Erratics 



Like the kames, glacial boulders or erratics are scattered over all 

 parts of the quadrangle except the typical sand plains. Their 

 absence from the sand plain belt is to be explained in much the 

 same way as the absence of the kames, that is after the boulders 

 were dropped by the melting ice they were covered by the delta 

 deposits so that they are scarcely ever seen except along the larger 

 stream courses where they have again been exposed by erosion. A 

 good many are present along the western front of tlie delta terrace 

 particularly in the vicinity of Greig. They are also strewn over 

 the Paleozoic rock area, even on the high land of Tug and Mohawk 

 hills. 



The erratics are mostly from the hard, resistant Precambric 

 formations and, as above pointed out, their presence on the high 

 western portion of the quadrangle strongly argues for a southerly 

 or southwesterly ice current at one time. The largest erratic ob- 

 served by the writer is one of quartzose syenite, already referred 

 to, which rests upon the Black River limestone about 2 miles north- 

 east of Boonville. This boulder measures about 27 feet across and 

 17 feet high. Another large one may be seen in the field about }i 

 of a mile east-northeast of Denley station. 



Glacial lakes 



A very interesting and extensive glacial lake occupied all of the 

 sand-flat country on the east side of Black river between Forest- 

 port and Lowville. It also extended somev/hat west of Black river 

 in the vicinity of Boonville, and to an unknown distance north of 

 Lowville. The former presence of this large lake is conclusively 

 shown by the great development of unquestioned delta deposits, 

 associated with clays, and the remarkably concordant altitudes of 

 the sand plains [see above]. These waters were impounded by the 

 waning lobe of ice in the Black river valley. The kames and drift 

 boulders along the western edge of the great delta deposit show an 

 ice contact from there ; also the absence of delta deposits on the 

 west side of the valley, under Tug hill, shows that the lake did not 

 extend that far west. Again the failure of any delta deposits to 

 reach out to or across the valley bottom also argues for ice occu- 



