6 PROCEEDINGS OF THE BOSTON MEETING 



of ouv continent, which, excepting the greater part of Alaska (probably exempted 

 from so high uplift), bore an ice-sheet of at least 4,000,000 square miles in area 

 and from one mile to probably two miles in thickness. 



Preglacial high Elevation known by Fiords and submerged Valleys 



WEST COAST OF NORTH AMERICA 



It was about one year ago that Professor George Davidson published his col- 

 lected observations of submerged valleys on the coast of California and Lower 

 California, as they were revealed by the soundings of the United States Coast 

 Survey.* From cape Mendocino southward along a distance of about 950 miles, 

 the submerged 100- fathom plateau, mostly five to fifteen miles wide, adjoining the 

 present shore, is indented by frequent deeply eroded old river valleys, some of 

 wdiich are continuations of present valleys on the land, while others are distinctly 

 traced from the verge of the submerged plateau inward to distances of only a mile, 

 or even less than a quarter of a mile, from the shore at projecting points where no 

 land valley now exists. About twenty of these submarine valleys are mapped by 

 Davidson, mostly ranging from 2,000 to 3,000 feet in depth at the verge of the pla- 

 teau, which on each side of the valley has a general depth of only 100 fathoms 

 (600 feet), with steep descent from this submerged former land margin into the 

 .abyssal ocean. But the maximum extent of the epeirogenic uplift at the time of 

 erosion of these valleys, as known by their deepest example, about a dozen miles 

 north of Monterey, was at least 868 fathoms (5,208 feet), this sounding of the Mon- 

 terey submerged valley being obtained in its deep seaward continuation, about 

 five miles beyond the general 100-fathom submarine contour and some twenty 

 miles off"shore. Within three miles on each side there the sea bed is less than 

 3,000 feet deep. In their general width, steepness of inclosing slopes, and occa- 

 sional tributary branches, these valleys have the usual forms of subaerial erosion; 

 so that to my mind they admit no other interpretation than that this large part of 

 the west side of North America was for a considerable time raised 3,000 to 5,000 

 feet above its present altitude. Before that time, for some preceding and appar- 

 ently longer period, the land altitude had been about 600 feet higher than now, 

 permitting the coast to be built out by fluvial and marine deposition to the verge 

 of the submarine i^lateau. The great uplift, according to Le Conte's discussion of 

 previous papers by Davidson on this subject, took place during Late Pliocene and 

 Pleistocene time, its culmination being attended with the continental glaciation.f 



The Californian submerged valleys lie south of the glaciated area, excepting as 

 that was represented by the anciently extended glaciers of the Sierra Nevada and 

 other more eastern high ranges of our great CordiUeran belt ; but the continental 

 elevation known for California doubtless was also continuous, in a varying, but 

 everywhere large, vertical amount, far to the north, through Oregon, "Washington, 

 British Columbia, and southern Alaska. From Puget sound northward the fiord- 

 indented coast, with its bordering series of many mountainous islands, separated 

 by channels that are continuations of the fiords, testify of such a formerly high 



♦ Proceedings of the California Academy of Sciences, third series, Geology, vol. i, pp. 7,3-10.3, with 

 plates iv-xii, June 2(i, 1897. See also the more recent paper by Harold W. Fairbanks, " Oscillations 

 of the Coast of California daring the Pliocene and Pleistocene " (Am. Geologist, vol. xx, pp. 21.3-245, 

 October, 1897), in which the literature of this subject, including earlier papers by Davidson, Le 

 Conte, Lavvson, and others, is carefully reviewed. 



t Bull- Geol. Soc. Am., vol. 2, 189t, pp. 323-330. 



