494 W. JJpham — Quaternary Changes of Leech. 



hills after they have been wetted by the rain, they glitter and shine 

 like the tinned roofs of the city of Montreal." ' 



Debarred by the shortness of the Postglacial epoch from attribut- 

 ing the Ice Age to the astronomic condition of maximum eccentricity, 

 so ably advocated by Croll, we must look for other causes of this 

 extraordinary geological period ; and these seem to be found in 

 great uplifts of the glaciated areas, of which for North America 

 Prof. Spencer has given an impressive review. The submarine 

 border of the continental plateau to depths of more than 3000 feet 

 is cut by valleys or channels, which if raised above the sea-level 

 would be fjords or canons. These can be no other than river- 

 courses eroded while the land stood much higher than now ; and its 

 subsidence evidently took place in a late geologic period, else the 

 channels would have become tilled with sediments. 



According to the United States Coast Survey charts, as noted by 

 Spencer, the bottom of a submerged valley just outside the delta of 

 the Mississippi is found by soundings at the depth of 3000 feet. 

 This valley is a few miles wide, and is bounded by a plain of the 

 sea-bed from 900 to 1200 feet above its floor. It thus appears that 

 the country north of the Gulf of Mexico has been raised for a short 

 time to a height of not less than 3000 feet; and it is important to 

 note in passing that an equal uplift would wholly close the Strait 

 of Florida, 2064 to 3000 feet deep, through which the Gulf Stream 

 now pours into the North Atlantic. 



The continuation of the Hudson Eiver valley has been traced by 

 detailed hydrographic survej's to the edge of the steep continental 

 slope at a distance of about 105 miles from Sandy Hook. Its outer- 

 most 25 miles are a submarine fjord three miles wide and from 

 900 to 2250 feet in vertical depth, measured from the crests of its 

 banks, which with the adjacent flat area decline from 300 to 600 

 feet in depth below the present sea-level. The deepest sounding in 

 this fjord is 2844 feet. 2 



An unfinished survey by soundings off the mouth of Delaware 

 Bay finds a similar valley submerged nearly 1200 feet, but not yet 

 traced to the margin of the continental plateau. 



Again, the United States Coast Survey and British Admiralty 

 charts, as Spencer states, record submerged fjord outlets from the 

 Gulf of Maine, the Gulf of Saint Lawrence, and Hudson Bay, 

 respectively 2664 feet, 3666 feet, and 2040 feet below sea-level. 

 The bed of the old Laurentian River from the outer boundary of 

 the Fishing Banks to the mouth of the Saguenay, a distance of more 

 than 800 miles, shown by Professor Spencer's map, is reached by 

 soundings 1878 to 1104 feet in depth. Advancing inland, the 

 sublime Saguenay fjord along an extent of about fifty miles ranges 

 from 300 to 840 feet in depth below the sea-level, while in some 

 places its boixlering cliffs, one to one and a half miles apart, rise 

 abruptly 1500 feet above the water. 3 



1 Id. p. 308. 



2 Rep. of U.S. Coast and Geodetic Survey, 1884, pp. 435-8, with map and profile; 

 also in Amer. Journ. Sci. in. vol. xxix. pp. 475-480, June, 1885. Compare Bulletin 

 Geol. Soc. Am. vol. i. 1889, pp 563-7. 



3 J. W. Dawson, "Note on the Post-Pliocene Geology of Canada," 1872, p. 41. 



