12 Barrett — Movements of the Strand L 



me 



and Talbot, carry a large proportion of ice-borne bowlders, too 

 large to be transported by the moderate development of river- 

 ice now carried by the streams. They indicate thicker ice and 

 a much colder period than at present.* These stages corre- 

 spond in general to what in New Jersey, Salisbury has named 

 the Bridgeton, Pensauken, and Cape May formations. 



The oldest glacial deposits of New Jersey, represented by 

 the patches of extra morainic drift, over the Triassic area are 

 preserved on flat hill tops which range from 200 to 220 feet 

 or more, in elevation. Some attenuation of the drift, ascribed 

 to creepage, is observed below these levels, but it is inferred 

 that the drift was laid down when the Triassic Plain was a gen- 

 tly undulating surface, corresponding with that whose dissected 

 remnants are now 225 to 275 feet above the sea. The larger 

 streams now flow at levels more than 100 feet below.f The 

 combination of evidence from Maryland and New Jersey sug- 

 gests strongly, though it lacks perhaps actual demonstration, 

 that certain early Pleistocene stages of cold climate and gla- 

 ciation occurred when the ocean level stood at the higher parts 

 of the phases of cyclic oscillation. The statement fails of com- 

 plete demonstration because the glacial deposits of New Jer- 

 sey may be somewhat different in age from the Sunderland 

 deposits of Maryland. The development of the plains at this 

 level by subaerial erosion during crustal rest had been accom- 

 plished, at least in large part, when the ice sheets ended consid- 

 erably north of their present limits, since the writer has iden- 

 tified baselevels of erosion at these levels in Connecticut. But 

 the glaciation took place either before these baseleveled sur- 

 faces of soft Triassic rock had been uplifted at all or had been 

 uplifted long enough to become dissected. The important 

 point, however, is that the development of the cold climates, 

 culminating in glaciation, does not appear to have required a 

 low level of the sea, or high elevatiou of the land of this 

 region. Such abstraction of ocean water as took place at 

 these times was, therefore, more or less compensated for by 

 occurring at the long submergent stages of the diastrophic 

 cycles. Nothing is said here as to the attitude of the land in 

 the centers of glacial accumulation. It is true that the central 

 regions of glaciation are now in a depressed condition, as shown 

 by the drowned topography. This may be the result of 

 a lack of complete isostatic recovery after the removal of the 

 ice load. This permanent depression is a factor, however, 

 which would not have operated in Maryland. In conclu- 

 sion, therefore, the evidence of the region marginal to gla- 



*G. B. Shattuck, The Pliocene and Pleistocene Deposits of Maryland; 

 Maryland Geological Survey, p. 85.. 1906. 



+ R. D. Salisbury, The Glacial Geologv of New Jersey, Final Eeport of 

 the State Geologist, vol. v, pp. 755-760, 1902. 



