Geology and Mineralogy. 497 



or that of the open sea not of great depths ; the temperatures of 

 the Caribbean Sea, Gulf of Mexico and western Atlantic, illus- 

 trated by deep-sea sections of the ocean, and a colored map of 

 the bottom temperatui'e-areas of both the North and South 

 Atlantic; the Gulf Stream; submarine deposits; the physiology 

 of the deep-sea life including the subject of the constitution of 

 sea-water, the degree of darkness of the depths, and other topics ; 

 and finally, descriptions of the West Indian fauna and sketches 

 of the characteristic deep-sea types through the various subdi- 

 visions of the animal kingdom from Vertebrates to Sponges, 

 which occupy the second volume and are illustrated by nearly 

 500 figures of species — the work in part of various zoologists whose 

 labors are acknowledged in the Introductory Chapters. 



The deep-sea soundings made under the direction of the IT. S. 

 Coast and Geodetic Survey in the West Indian seas have brought 

 to light some marvellous facts with regard to depths,' which Mr. 

 Agassiz has finely illustrated by maps as well as descriptions. 

 The facts were for the most part first announced in 1884 by Mr. 

 Hilgard, the superintendent of the Coast Survey, citations from 

 whose paper are introduced. A fact of special interest is the great 

 and abrupt depth close along the north shore of the West Indian 

 range of islands, " the 2000-fathom line nowhere more than 14 miles 

 from laud," and in one place 1976 fathoms "only 2-J- miles out, 

 a declivity of 38° ; and, in this line, a depression over 4000 fathoms 

 deep within 75 miles of Porto Rico, the deepest sounding giving 

 4561 fathoms, indicating a mean submarine slope from the Porto 

 Rico coast-line of 1:14. Further, from this deep depression a 

 trough of 2000 fathoms (the soundings 2000 to 2326 fathoms) 

 extends westward by the north shore of San Domingo, between 

 it and the reef islands north, with slopes part of the way on 

 either side of 1: 8-J; and this deep trough diminishing probably 

 to 750 fathoms on the ridge between San Domingo and Cuba, 

 commences again on nearly the same course close by the most 

 southern Cuban shore (within 25 miles) by a trough of 3138 and 

 3180 fathoms, and is continued westward by two other areas of 

 3428 and 3206 fathoms pointing down to the southwest angle of 

 the west-Caribbean or Cuban Sea north of Honduras. Agassiz's 

 maps, figs. 56 and 57, show these troughs and the view on page 

 94 of a model of the Gulf made under Mr. Hilgard's direction, 

 exhibit it still more strikingly through the greatly exaggerated 

 vertical scale. Mr. Agassiz suggests one explanation for the 

 origin of the great depths and correlately for mountains on the 

 borders of the ocean on page 132, and another for some of the 

 depressions on page 104. 



Another feature in the sea-bottom topography illustrated by 

 the soundings is the absence, between a point just south of Cape 

 Hatteras and the Bahamas of that steep side-slope of the Atlan- 

 tic basin along the 100-fathom line which prevails north of the 

 Cape. In place of it, there is a very gradual inclination outward 

 to the 600-fathom line and then a dip off to greater depths, mak- 



