238 



SCIENCE 



[N. S. Vol. XXXVII. No. 946 



raines, and the large number of Postglacial 

 ravines. 



The purpose of this writing is to utilize 

 this remarkable display of Pleistocene phe- 

 nomena in illustration of the glacial history 

 and in brief discussion of some problems in 

 the philosophy of glaciation. 



MULTIPLE GLACIATION 



The accepted facts of multiple glaciation 

 in the Mississippi basin coupled with 

 proofs of Prewisconsin drift in Pennsyl- 

 vania and New Jersey and on Long Island, 

 with accumulating evidences in New Eng- 

 land, demands the theoretical acceptance of 

 at least dual glaciation for New York state. 

 But the positive proof, in the field, of a Pre- 

 wisconsin ice sheet has not been found. In 

 several localities the deeper till is so unlike 

 the upper till that it strongly suggests a 

 separate origin. Some singular topographic 

 features are not satisfactorily explained 

 without appeal to the earlier ice invasions. 

 The Rutland Hollow, east of Watertown, is 

 an example. Many erosion features, spe- 

 cially in the St. Lawrence district, seem in- 

 consonant with the work of the latest ice.- 

 However, we have found no example of 

 interglacial or warm-climate deposits inter- 

 bedded in the till. Such should be ex- 

 pected and sought, but at present we can 

 only say that multiple glaciation in New 

 York, at least north of Long Island, is 

 quite certain in our philosophy but that it 

 remains unproven in observation. 



Although our glacial phenomena in New 

 York are doubtless not the effects of merely 

 the latest or Laurentian ice sheet, the latter 

 so strongly dominates that for purpose of 

 this writing it is impracticable to attempt 

 discrimination, and unless specially noted 

 it will be understood that reference is to 

 the latest, or Wisconsin, glaciation. 



" For discussion of this subject see N. Y. State 

 Museum Bulletins, No. 145, pp. 164-172; No. 160, 

 pp. 17-18. 



LAURENTIAN ( LABEADORIAN ) ICE BODY 



The reach or extent of the latest ice sheet 

 has long been known in a general way 

 through the early work of Upham, Lewis 

 and Wright in tracing the terminal mo- 

 raine. In later years the stretches of the 

 terminal moraine which lie in New York 

 have been reexamined, on Long Island by 

 Woodworth and Puller and Yeatch, and in 

 Cattaraugus county by Leverett. There 

 are two small areas in the state which the 

 ice sheet did not cover, the south side of 

 Long Island and the district partly en- 

 closed by the northward bend of the Alle- 

 ghany River. 



At its maximum the ice sheet covered the 

 highest points in the state, the Adirondack 

 (5,344 feet) and the Catskill (4,205 feet) 

 mountains. Judging from the Antarctic 

 and Greenland ice caps the surface of the 

 Laurentian shield was a low dome of fairly 

 uniform curvature, uninfluenced by the ir- 

 regularities of the submerged land surface. 

 Our only means of estimating the thickness 

 of the ice cap is by assuming a gradient of 

 the surface slope, as suggested by observa- 

 tions on the existing polar ice fields. Such 

 data, however, can be safely used only in a 

 suggestive way when applied to the Lau- 

 rentian ice shield, because the difference in 

 latitude must be an important factor. The 

 border of our ice field, in latitude 41 to 44 

 degrees, was subjected to so much greater 

 solar radiation and consequent higher tem- 

 peratures, with heavy precipitation and 

 rains, that it must have had increased 

 plasticity and resultant mobility, giving 

 the surface slope diminished gradient. 

 But on the other hand the snow supply 

 over the central area or alimentation 

 ground of the ice field must have been 

 greater than over the polar fields, which 

 might give greater depth and steeper 

 gradients toward the interior of the field. 

 The anticyclonic winds over the ice cap, re- 



