208 J. W. SPEXCER — SUBMARINE VALLEYS 



are mapped, but its completion has been postponed, while the writer 

 was engaged on other West Indian and Central American investigations, 

 the results of which have appeared from time to time. In these later 

 papers the details of the submarine topography are elaborated, but no 

 additional studies along the Atlantic coast have been completed, though 

 there is a fragmentary notice of some of the valley-like features * While 

 the key of the subject is among the West Indian islands and off the coast 

 of Florida and Georgia, the features so repeat themselves farther north- 

 ward, along the great submarine slope, that they are worthy of careful 

 consideration. So also in the north Atlantic, between Greenland and 

 Europe, the region is full of interest. Although the soundings off the 

 European coast are not made along the most satisfactory lines, or car- 

 ried far enough, yet the studies of Professor Edward Hull f show the gen- 

 eral extension of the deep valleys down the continental slope on the 

 eastern side of the Atlantic basin, and Mr Warren Upham made other 

 studies off the American coast. J The submarine basins have been 

 widely studied, but the deep incisions of the great continental slopes 

 have been generally overlooked, although several European writers, in 

 various languages, have described special features, and it is these features 

 which form the present theme. Since these pages were in proof, Dr F. 

 Nansen, of Norway, has shown me similar studies in preparation. 



Submerged Plains off the eastern Coast of America § 



The present topic begins with cape Hatteras and extends to the mar- 

 gin of the Newfoundland banks. Off cape Hatteras the submerged 

 coastal plains are reduced to a breadth of less than 25 miles. They 

 widen to 85 miles off New Jersey, and again south of Rhode Island 

 (Marthas Vineyard), and to considerably more between these localities, 

 especially in front of New York harbor, while they extend 300 miles 

 southeast of Newfoundland. From cape Hatteras to above the latitude 

 off the mouth of Chesapeake bay, the outer edge of the submarine plains is 

 taken to be a line at a depth of 200 to 250 feet below sealevel. Beyond 

 that point it is fringed with a somewhat steeper slope or in places a lower 

 terrace, whose outer margin has a depth of 400 to 450 feet. The chart 

 contour of 600 feet occurs everywhere beyond the margin of the sub- 



*Read before the Brit. Assoc. Adv. Sci., 1897; Geol. Mag., London, Dec. iv, vol. v. (1898), pp. 

 35-37. 



t" Submerged terraces and river valleys bordering the British isles;" "Suboceanic terraces 

 and river valleys off the coast of western Europe ; " "Physical historj' of the Norwegian fjords," 

 and other papers read before the Victoria Institute and appearing in the Transactions from 1898 

 till the present year. 



X Bull. Geol. Soc. Am., vol. 1, 1889, pp. 563-567. 



g See U. S. Hydrographic Charts, no. 1411 and no. 21a. 



