MUSEUM OF COMPARATIVE ZOOLOGY. 59 



due not only to the improvements suggested in the apparatus by Cap- 

 tain Sigsbee, by Lieutenants Ackley and Sharrer, and by Messrs. Jacobi 

 and Moore, but also to the great care taken by the officer of the deck in 

 handling the " Blake " during the progress of a haul. With a vessel of 

 the size of the " Blake," excellent judgment was necessary while working 

 in a seawa}^, and that we incurred so few accidents is entirely due to the 

 interest taken in the expedition by the officers, and the devices con- 

 stantly suggested by them for overcoming the difficulties we encountered 

 in this novel work. 



The accompanying figures (PI. I.) will explain the modifications intro- 

 duced in the dredge and trawl. 



A small map of the Gulf of Mexico, with the 100, 500, 1,000, 1,500, 

 1,800, and 2,000 fathom curve, has been prepared at the Coast Survey 

 Office in order to give a general sketch of the Hydrography of the Gulf 

 of Mexico. Only a small number of the soundings of the " Blake " are 

 here introduced ; they are selected from an immense number plotted 

 during the last four years. The map speaks for itself, and I need only 

 call attention in a general way to the principal features of the bottom. 

 The most striking characteristics of the Gulf are the two great banks 

 extending the one to the west of Florida peninsula and northward of the 

 Florida Reef, the other northward of the peninsula of Yucatan, the 100- 

 fathora line in both cases running in a general way parallel to the shore 

 line and forming the edge of the steep slopes of the deeper parts of the 

 central portion of the Gulf of Mexico. The rapidity with which the 

 depth increases is very strikingly shown to the north of the Tortugas, and 

 to the northward and westward of Alacran Reef, by the proximity of the 

 100 and 1,800 fathom curves, the eastern and southern edges of the 

 central basin of the Gulf of Mexico having thus very steep sides, while 

 the western and northern slopes are far more gradual. The north slope 

 off Cuba is also quite abrupt, while the southern slope of the Florida 

 Reef into the trough of the Gulf Stream is comparatively gentle. The 

 soundings taken in 1878 have developed a remarkable extension of the 

 southeast end of the Yucatan Bank within the 1000-fathom curve, in 

 the direction of the Tortugas, with a depth of 500 to 700 fathoms for 

 over one hundred miles. This will be shown in a more detailed map 

 hereafter. 



The greatest depth of the Yucatan Channel is somewhat more than 

 1,100 fathoms, so that tlie temperature of all the water which finds its 

 way into the Gulf of Mexico is necessarily at its deepest point (2,119 

 fathoms) only the temperature of the bottom of the Straits of Yucatan 



