220 THREE CRUISES OF THE " BLAKE." 



the water which finds its way into the Giilf of Mexico is neces- 

 sarily at its deepest point (2,119 fathoms) only that of the bot- 

 tom of the Straits of Yucatan (1,127 fathoms), namely, 39V F. 

 This can only have the temperature of the deepest ridge sepa- 

 rating the eastern Caribbean from the Atlantic (392^' F.). The 

 depth of the channel through ^yllich the water of the Gulf ul- 

 timately finds its outlet is very much less (344 fathoms), and 

 the Straits of Bernini, with a cross-section of not more than 

 eleven square miles, are not half the width of the Straits of 

 Yucatan. The temperature of the water at the bottom of the 

 Gun Key Channel is much higher (see Fig. 158), with a far 

 greater surface velocity than that of the current flowing into the 

 Gulf of Mexico through the Straits of Yucatan. 



It is therefore incredible that, with this huge mass of water 

 pouring into the Gulf of Mexico, there should be anything like 

 a cold current forcing its way up-hill into the Straits of Florida, 

 as has been asserted on theoretical gTounds. The channel at 

 Gun Key can only discharge the surplus water by having a great 

 velocity. 



The soundings made by the " Challenger " off Sombrero on 

 their line from Sombrero to Teneriffe, as well as the soundings 

 north of St. Thomas on the line from St. Thomas to Bermudas 

 (see Fig. 170), were fortunately both taken in March, at about 

 the same time with those of Commander Bartlett. 



On comparing the soundings taken by the " Blake " off Som- 

 brero (Fig. 144), twenty miles from shore, with those of the 

 "Challenger" (see Fig. 170), three hundred miles from shore, 

 we find the surface temperature observed by the " Blake," and 

 at a depth of fifty fathoms, slightly higher (2^), at 100 fathoms 

 2° less, at 200 fathoms 1"" less. The temperature of 50° is 

 reached at a depth of 350 fathoms by the " Challenger ; " at 

 300 by the " Blake." The " Blake " observed 46° at 400 fath- 

 oms, the " Challenger " 45° at 425 fathoms, and at a depth of 

 700 fathoms both the " Challenger" and " Blake" record a tem- 

 perature of 40°. The " Blake " serials show 40° to a depth of 900 

 fathoms, while the " Challenger " has at the same depth 39°. 

 At the deepest point on that line (2,558 fathoms) the " Blake " 

 observed a temperature of 36°, while at the same depth the 



