142 PROP. E. HULL, LL.D,, P.K.S., P.G.S., ON 



Plateau."* Off Cape Hatteras the breadth of the Continental 

 Shelf is 15 miles, but it increases to 100 miles off the coast 

 of New England, and to 200 miles off the coast of Maine.f 

 The slope from 100 to 500 fathoms is often so steep, that the 

 two contours approach very close together. The outer 

 slope of the Blake Plateau is also remarkably steep in some 

 places, so that the contours of 500 and 1,000 fathoms come 

 almost into contact on the charts, as, for example, off Cape 

 Hatteras. These two submarine terraces, with their marginal 

 slopes, are continued around the West Indian Islands, the 

 Gulf of Mexico, and the Caribbean Sea, In the Gulf of 

 Mexico the Continental Shelf, shown by the 100-fathom line, 

 stretches for long distances from the shore, especially from 

 the Northern Coast and Yucatan, where it is distant 150 miles 

 from the coast. Inside Florida the distance is about the 

 same ; and as the 100-fathom contour represents very closely 

 the general continental margin, the massifs of the peninsulas 

 of Florida and of Yucatan have more than twice their 

 apparent breadth.| 



These two terraces, continuous as they are throughout 

 such a great extent of coast-line, and with levels so generally 

 uniform, naturally suggest formation during one or more 

 periods of emergence and depression, interrupted by pauses ; 

 and this impression has been corroborated by the further 

 determinations of Professor J. W. Spencer, drawn from a 

 careful delineation of the physical features of these submarine 

 terraces and their marginal slopes, resulting in a remarkable 

 advance in our views of suboceanic geography.§ Briefly 

 stated Professor Spencer shows that most of the river-valleys 

 of the American continent opening into the Atlantic or the 

 Gulf of Mexico are continued under the ocean, traversing 

 first the Continental Shelf and then passing onwards through 

 deep and wide " embayments " to the Blake Plateau, which 

 they also traverse, until finally lost in the abyssal region, 



* Three Onuses of the ''Blake" (1888). 



t Agassiz, ibid., p. 95. 



J Ibid., p. 102. These terraces are represented by shading on the 

 accompanying map (Plate). 



§ "Eeconstruction of the Antillsean Continent," Bull. Geol. Soc, Amer., 

 vol. vi (1895) ; also, "Terrestrial Submergence of the South-east of the 

 American Continent," Ibid., vol. v (1893). A copious review of Prof. 

 Spencer's, Memoirs by Mr. A. J. Jukes-Browne, appeared in the 

 Geological Magazine, April, 1895. Startling as are the deductions of 

 Prof. Spencer, I am not aware that they are contested by any American 

 geologist of eminence. 



