210 Prof. J. W. Spencer — High Continental Elevation. 



rainfall could so increase the volume of the discharge as to remove 

 all the deposits which now fill the old valley, much less excavate 

 the original and immense canon. A vastly greater elevation of the con- 

 tinent would be necessary. Even were the whole continent uni- 

 formly elevated 630 feet together with the remainder of the unknown 

 depth of the ancient Mississippi River at New Orleans, the canon of 

 the upper part of the river would require a still greater relative 

 elevation of the northern country, in order to give sufficient channel- 

 ling power to the flowing waters. But the slope of the floor of the 

 buried valley is much less than that of the modern one, as was formerly 

 shown by the author. 1 Here, again, is the proof that the country drained 

 by the upper waters of the Mississippi once stood much higher than 

 at present, relatively, to that of the region nearer its mouth. Of 

 the amount, which was at least many hundreds of feet, we have no 

 absolute measurement. Nor can we ascertain it by calculation, for 

 there is no registry of the excess of the amount of rainfall, during 

 the epoch of the greatest sculpturing, over that of the present day. 



"Whilst these records of the Mississippi, which have been only 

 partially deciphered, do not furnish all the desired information, yet, 

 as far as they go, they are invaluable. 



Passing from the buried channel of the Mississippi to its con- 

 tinuation, now submerged beneath the waves of the Gulf of Mexico, 

 we find evidence indicating such a stupendous continental elevation 

 as to be almost incredible were it not supported by collateral 

 evidence, upon both the Pacific and Atlantic -coasts. The soundings 

 off the coast of the delta of the Mississippi indicate the outer 

 margin of the continental plateau as submerged to a depth of 3600 

 feet, 2 indented by an embay men t of another hundred fathoms in 

 depth, at the head of which there is a valley, a few miles wide, 

 bounded by a plateau from 900 to 1200 feet above its floor. This 

 valley is now submerged to a depth of over 3000 feet, and is 

 the representative of the channel of the ancient Mississippi River, 

 towards which it leads. 



On the Pacific coast, in the region of Cape Mendocino, Prof. George 

 Davidson has identified three valleys now submerged to from 2400 

 to 3120 feet, and several of inferior depth. These measurements 

 are those of the valleys where they break through the marginal 

 plateaux of the continent, at about six miles from the present shore, 

 where it is submerged to the depth of a hundred fathoms. 3 



The soundings along the Atlantic coast reveal similar deep fjords. 

 The extension of the Hudson River beneath the Atlantic waters, 

 known long since, is traceable to the margin of the continental 

 acquiring a depth of 2844 feet, in front of which the soundings 

 plateau, show a bar, covered with mud, which, however, is now 

 submerged to the depth of only 1230 feet. 4 



The as yet unpublished soundings off the mouth of the Delaware 



1 J. W. Spencer, "Warping of the Earth's Crust," etc., Am Nat., Feh. 1887. 



2 J. "W. Spencer, "The Miss. River, etc." 1884. See also Coast Survey Charts. 



3 Prof. George Davidson, Bull. Cal. Acad. Sc, ii. 6, 1887, p. 265. 



* A. Lindenkohl, Appendix, No. 13, Kept. U.S. Coast Survey, 1884, pp. 270-273. 



