506 F. G. CLAPP GLACIAL PERIOD IN NEW ENGLAND 



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3. Degree of oxidation 525 



4. Sections sliowing botli this and a more recent till of differ- 



ent character 520 



Coarse gravels 520 



General description 520 



Relations and correlations 527 



Distinction from Wisconsin gravels 527 



1. Erosion before deposition of overlying clay 527 



2. Occurrence of till overlying the gravels 528 



3. Erosion and folding of gravels by overriding ice 528 



Fossiliferous marine clays ("Leda clay") 528 



Use of term "Leda clay" 528 



General description 529 



Distribution 529 



Fossils 530 



Distinction between high-level and low-level clays 531 



Relations of the high-level clay 531 



Correlations 532 



Evidence that this clay is not of Wisconsin age 532 



1. Degree of oxidation 533 



2. Oxidation of buried clay surfaces which were formed by 



subaerial erosion 534 



3. Occurrence of overlying till and moraiual deposits 530 



4. Folding and erosion due to action of overriding ice 539 



5. Reworked upper part of some clays 541 



6. Older topography and greater elevation of some clays than 



of certain clays believed to be of Wisconsin age 542 



7. Occurrence of overlying buried soils 544 



Wisconsin till 544 



General description 544 



Evidence of Wisconsin age 545 



1. Uppermost till in the region ; 545 



2. Difference in character from lower tills 545 



3. Occurrence of underlying stratified deposits 540 



4. Slight surface oxidation 547 



5. Veneers of this till over Montauk till 548 



Drumlins are believed to antedate pre-Wiseonsin clay 549 



Distinction from beach deposits 551 



Distinction from iceberg-dropped material 551 



Strife of diverse directions 552 



Wisconsin retreatal deposits. 



t)i)-: 



Wisconsin clays 553 



Post-Wisconsin or late Wisconsin deposits 553 



Arguments opposing the oscillating-ice-front theory 5.54 



Summary 555 



