1 8 NEW YORK STATE MUSEUM 



the Adirondacks along the International boundary to Lake Cham- 

 plain. The customary classification of glacial deposits for the 

 purpose of geologic mapping breaks down in this area by reason 

 of the modification of the deposits through action of sea waves and 

 currents. The problem of how best to map these modified glacial 

 deposits has perhaps not yet been satisfactorily solved. The prob- 

 lem is a particularly difficult one by reason of the varying degree 

 of alteration and rearrangement of the original accumulations. 

 Some parts of the area display a typical glacial topography and 

 underlying structure of the materials ; yet other districts show the 

 glacial deposits entirely recomposed in beaches, bars, and offshore 

 sediments. These features are not always clear; there are large 

 tracts in which no distinctive surface characters exist and in which 

 the deposits can only be discriminated on such broad groupings as 

 stratified, gravelly, sandy or clayey. This results in the necessity 

 of colormg large areas as undifferentiated glacial and marine or 

 glacio-marine gravels and sands. 



On the Rouse Point quadrangle there is a marked belt of sandy 

 beach deposits about the hills at levels between i8o and 220 feet 

 above sea level. Along the northern border of the area in the vicin- 

 ity of Champlain village, pocket beaches occur at lower levels. 

 Marine shells have been found in sufficient abundance to give some 

 idea of the fauna. There is a noticeable abundance of ]\I y a 

 arenaria at these lower levels, but it is absent at the higher 

 stands of the sea. Either this mollusk reached the area relatively 

 late or lived only in the deeper offshore stations. Owing to its 

 abundance in shallow surface deposits I am inclined to the view that 

 it migrated into the Champlain area much later than S a x i c a v a 

 r u g o s a and Macoma greenlandica. If this be true it 

 may be possible to differentiate locally these life zones. M y t i 1 u s 

 e d u 1 i s also appears in abundance and in an excellent state of 

 preservation at these lower levels, as on the Isle la Motte. 



The field work indicates pretty clearly that a morainal belt extends 

 southeastward across the Mooers area towards Chazy, indicating a 

 protrusion of the ice front into the Champlain embayment at a late 

 stage, possibly as an ice advance after the sea once got into the 

 area. Unless the unfossiliferous clays about East Beekmantown 

 and near the lake shores in that vicinity and around Alburg can be 

 referred to the lacustrine stage, no deposits are recognized which 

 can be definitely referred to the glacial lake waters which preceded 

 the marine invasion in this field, nor have any Prewisconsin drift 

 deposits been found. 



