40 THE PHYSICAL GEOGRAPHY OF THE SEA. 



minutest organism that the most powerful microscope can detect 

 among the impalpable particles of sea-dust. This effect of diur- 

 nal rotation will be frequently alluded to in the pages of this work. 



46. In its course to the north, the Gulf Stream gradually trends 

 more and more to the eastward, until it arrives off the Banks of 

 Newfoundland, where its course becomes due east. These banks, 

 it has been thought, deflect it from its proper course, and cause it 

 to take this turn. Examination will prove, I think, that they are 

 an effect, certainly not the cause. It is here that the frigid current 

 already spoken of (§ 11), with its icebergs from the north, are met 

 and melted by the warm waters of the Gulf. Of course the loads 

 of earth, stones, and gravel brought down upon them are here de- 

 posited. Captain Scoresby, far away in the north, counted five 

 hundred icebergs setting out from the same vicinity upon this cold 

 current for the south. Many of them, loaded with earth, have been 

 seen aground on the Banks. This process of transferring deposits 

 for these shoals has been going on for ages ; and, with time, seems 

 altogether adequate to the effect described. 



The deep sea soundings that have been made by vessels of the 

 navy (Plate XI.) tend to confirm this view as to the formation of 

 these Banks. The greatest contrast in the bottom of the Atlantic 

 is just to the south of these Banks. Nowhere in the open sea has 

 the water been found to deepen so suddenly as here. Coming 

 from the north, the bottom of the sea is shelving ; but suddenly, 

 after passing these Banks, its depth increases by almost a precip- 

 itous descent for many thousand feet, thus indicating that the 

 debris which forms the Grand Banks comes from the north. 



47. From the Straits of Bemini the course of the Gulf Stream 

 (Plate VL) describes (as far as it can be traced over toward the 

 British Islands which are in the midst of its waters) the arc of a 

 great circle as nearly as may be, only the thread or axis of the Gulf 

 Stream does not generally go quite as far north as the great circle 

 would. Such a course as this is the course that a cannon ball, 

 could it be shot from these straits to those islands, would take. 



If it were possible to see Ireland from Bemini, and to get a can- 

 non that would reach that far, the person standing on Bemini and 

 taking aim, intending to shoot at Ireland as a target, would, if the 

 earth were at rest, sight along the plane of a great circle, for the 

 path of the ball would be in such a plane. 



