ANTARCTIC CRUISE. 355 



retain the huge masses of ice, by their being attached by their lower 

 surfaces instead of their sides only. 



Much inquiry and a strong desire has been evinced by geologists, 

 to ascertain the extent to which these ice-islands travel, the boulders 

 and masses of earth they transport, and the direction they take. 



From my own observations, and the information I have collected, 

 there appears a great difference in the movements of these vast 

 masses; in some years, great numbers of them have floated north 

 from the Antarctic Circle, and even at times obstructed the navigation 

 about the capes. The year 1832 was remarkable in this respect; 

 many vessels bound round Cape Horn from the Pacific, were obliged 

 to put back to Chili, in consequence of the dangers arising from ice ; 

 while, during the preceding and following years, little or none was 

 seen : this would lead to the belief, that great changes must take 

 place in the higher latitudes, or the prevalence of some cause to 

 detach the ice-islands from the barrier in such great quantities as to 

 cover almost the entire section of the ocean, south of the latitude 

 50° S. Taking the early part of the (southern) spring, as the time of 

 separation, we are enabled to make some estimate of the velocity with 

 which they move : many masters of vessels have met them, some six 

 or seven hundred miles from the barrier, from sixty to eighty days 

 after this period, which will give a near approximation to our results 

 heretofore stated. 



The season of 1839 and '40 was considered as an open one, from 

 the large masses of ice that were met with in a low latitude, by 

 vessels that arrived from Europe at Sydney : many of them were seen 

 as far north as latitude 42° S. 



The causes that prevail to detach and carry them north, are 

 difficult to assign. I have referred to the most probable ones that 

 would detach them from the parent mass in their formation. Our 

 frequent trials of currents, as has been stated, did not give us the 

 assurance that any existed ; but there is little doubt in my mind 

 that they do prevail. I should not, however, look to a surface cur- 

 rent as being the motive power that carries these immense masses 

 at the rate they move ; comparatively speaking, their great bulk is 

 below the influence of any surface current, and the rapid drift of 

 these masses by winds is still more improbable. Therefore I conceive 

 we must look to an under current as their great propeller. In one trial 

 of the deep-sea thermometer, we found the temperature beneath four 

 degrees warmer than the surface. Off Cape Horn the under tempera- 



