312 R.A.DALY — ^OSCILLATIONS OF LEVEL 



worth, the zero isobase is north of New York City; Leverett and Taylor 

 are inclined to the same view. If it be correct, the deformation of the 

 Passaic basin would be a striking proof of downwarping in a belt outside 

 the area of Eecent uplift. 



A parallel case is found in former Lake Missoula of northwestern 

 Montana. This late Glacial lake lay in the belt peripheral to the Cor- 

 dilleran ice-cap and owed its origin to damming by powerful tongues of 

 ice flowing southward from British Columbia. According to Campbell, 

 the highest strand of Lake Missoula has been tilted strongly to the north- 

 westward, showing "a depression of the earth's crust in that direction 

 since the breaches were formed, or a rise in the surface to the southeast. 

 Such a movement is also indicated by the recent canyon cut by Clark 

 Fork between Missoula and the mouth of Saint Eegis River." ^^ The 

 highest lake strand south of Missoula is now at the 4,200-foot contour, 

 and not far upstream from Pend d'Oreille Lake is at or near the 3,500- 

 foot contour. The average tilting is thus nearly 6 feet to the mile for an 

 air-line distance of 120 miles. Is this Recent crustal warping due to 

 isostatic collapse of the temporary marginal bulge, which had been forced 

 up by the weight of the Cordilleran ice-cap ? 



SUBMARINE HUDSON CHANNEL 



Merrill, Woodworth, and others have shown that the land near the 

 mouth of the Hudson River was higher at some post- Glacial stage than 

 it is now.^* Long ago, Dana, Upham, and others explained the submarine 

 channel of the Hudson across the continental shelf by the erosion of this 

 river when it had a lower baselevel. The depth of the channel is prob- 

 ably too great to be attributed to corrasion when the ocean-level fell 

 because of abstraction of water to form the Pleistocene ice-caps. On the 

 other hand, the channel may have been cut as the continental shelf rose, 

 to form Georges Bank Land. In that case the cutting could have been 

 begun by an extended Hudson River (seeking the new Glacial baselevel 

 of a sinking ocean surface), to be continued in the soft material of the 

 shelf after the upwarping began. For a time, then, the lower Hudson 

 would have been in the class of antecedent rivers. Subsequent rise of 

 general ocean-level, followed by downwarping, would account for the 

 final drowning of the valley (see plate 14). 



In common with other hypotheses, this one encounters the difficulty of 



"M. R. CampbeU and others : U. S. Geol. Survey Bull. 611, 1915, footnote on pp. 

 134-136. See map opposite p. 144 and also ,T. T. Pardee, Jour. Geol., vol. 18, 1910, p. 

 376. 



14 F. J. H. Merrill : Am. Jour. Sci., vol. 41, 1891, p. 460. 

 J. B. Woodworth : Bull. 84, New York State Museum, 1905. 



