554 F. G. CLAPP GLACIAL PERIOD IN NEW ENGLAND 



as a local center. The glaciers may have extended 20 miles or more from 

 the mountain. Evidences of similar local glaciers have been discovered 

 by Hitchcock * in the White mountains of Xew Hampshire and the Green 

 mountains of Vermont, and by Kich f in the Catskill mountains of New 

 York. 



ARGUMENTS OPPOSING THE OSCILLATING ICE-FRONT THEORY 



The principal objection advanced to the views outlined in this paper 

 has been the claim that the phenomena could all be explained by the 

 theory that the Wisconsin ice-sheet had an oscillating margin, a supposi- 

 tion which apparently would obviate the necessity of postulating any pre- 

 Wisconsin glacial or interglacial epochs. While it is true that many of 

 the features observed could be explained in that way, and the probability 

 still remains that such may be the origin of some slight deformations 

 and of certain instances of till over local stratified deposits, the following 

 facts oppose the belief that an oscillating ice-front could be responsible 

 for the great majority of phenomena observed : 



1. Some of the deformations of stratified beds are on a larger scale 

 than any likely to be produced by a merely local re-advance. 



2. Many exposures of till overlying marine clay and of contorted clay 

 are situated scores of miles south of the northern limit of the high-level 

 clays, and the fact that the ice must have retreated sufficiently to allow 

 deposition of these clays before the re-advance took place means a consid- 

 erable time interval. 



3. The common weathered zone at the top of the sand or clay and 

 below the overlying till could be caused only by an interglacial period of 

 some thousands of years. The deep weathering and other features of the 

 oldest tills, described on pages 514-516 and 525-526, preclude the proba- 

 bility of, their having been formed during Wisconsin oscillations. 



4. Under the oscillation theory it is impossible to account for the 

 prevalence of the unstratified sandy or stony upper portion of the high- 

 level clays. 



5. If the hypothesis of oscillating ice-front and post-Wisconsin age of 

 all the clays were true, it would be necessary to explain the weathering 

 and erosion of the high-level clays on the basis of a post-Wisconsin rise 



* C. H. Hitchcock : Proc. Am. Assoc. Adv. Sci., vol. xiii, 1859, pp. 329-335 ; Prelim- 

 inary Report on Nsit. Hist, and Geol. of Maine (Sixth Ann. Rept. Maine Board of Agri- 

 culture, 1861), p. 393; Geology of New Hampshire, vol. i, 1874, pp. 539-544; Proc. Am. 

 Assoc. Adv. Sei., vol. xxiv, part 2, 1875, pp. 92-96; Geology of New Hampshire, vol. iii, 

 1878, pp. 181-340; Bull. Geol. Soc. Am., vol. 7, 1896, pp. 3, 4. 



t J. L. Rich : Local glaciation in the Catskill mountains. Journal of Geology, vol. 

 xlv, 1906, pp. 113-121. 



