620 report— 1878. 



for at these points of junction with the drift-current of the westerlies, the 

 isobathy therms are slightly deflected, to the southwards, and it is opposite these 

 points of junction that we have comparatively open sea and penetrable notches in 

 the southern pack. But we have not only the presumed effect of this transfer of 

 warmer water to the southwards, we were able to detect its presence in the 

 Challenger by the thermometer. Referring to the result of a serial temperature 

 sounding on the 14th of February 1874, with a surface temperature 6f 29° F. at 

 a depth of from 300 to 400 fathoms, there is a band of water at a temperature 

 more than half a degree above the freezing-point, That this comparatively warm 

 water is coming from the north there is ample proof. We traced its continuity 

 with a band at the same depth gradually increasing in warmth to the northward, 

 and it is evident that its heat can be derived from no other source, and that it must 

 be continually receiving new supplies, for it is overlaid by a band of colder water, 

 tending to mix with it by convection. 



It is, of course, possible that these warm currents may by coincidence be 

 directed towards those notches already existing in a continental mass of land ; but 

 such a coincidence would be remarkable, and there is certainly a suggestion of the 

 alternative that the " continent " may consist to so great an extent of ice as to be 

 liable to have its outline affected by warm currents. 



In high southern latitudes it seems that all the icebergs are originally tabular, 

 the surface perfectly level and parallel with the surface of the sea, a cliff about 230 

 feet high bounding the berg. The top is covered with a layer of the whitest 

 snow ; now and then a small flock of petrels take up their quarters upon it, and 

 trample the soil some few square yards, but after their departure one of the frequent 

 snow showers restores it in a few minutes to its virgin whiteness. The upper part 

 of the cliff is pale blue, which gradually deepens towards the base. When looked 

 at closely, the face of the cliff is seen to be traversed by a delicate ruling o'f faint 

 blue lines, the lines being more distant from one another above and becoming 

 gradually closer. The distance between the well-marked lines near the top of a 

 berg may be of a foot or even more, while near the surface of the water it is not 

 more than two or three inches, and the space between the blue lines have lost their 

 dead whiteness and have become hyaline or bluish. The blue lines are very 

 unequal in their strength and in their depth. of colouring; sometimes a group of 

 very dark lines gives a marked character to a part of a berg. Between the 

 stronger blue lines near the top of the cliff a system of closer lines may be 

 observed, marking the division of the ice by still finer planes of lamination ; but 

 in the narrower spaces near the water-line they are blended and lost. The blue 

 lines are the sections of sheets of clear ice ; the white intervening bands are the 

 sections of layers of ice where the particles are not in such close contact — ice 

 probably containing some air. 



The stratification in all these icebergs is, I believe, originally horizontal and 

 conformable, or very nearly so. In many, while melting and beating about in the 

 sea, the strata become inclined at various angles, or vertical or even reversed ; in 

 many they are traversed by faults, or twisted, or contorted, or displaced ; but I 

 believe that all deviations from a horizontal arrangement are due to changes 

 taking place in the icebergs themselves. 



I think there can be no doubt, from their shape and form, and their remarkable 

 uniformity of character, that these great table-topped icebergs are prismatic blocks 

 riven from the edge of the great antarctic ice-sheet. I conclude, therefore, that 

 the upper part of the iceberg, including by far the greater part of its bulk, and 

 culminating in the portion exposed above the surface of the sea, was formed by 

 the piling up of successive layers of snow during the period, amounting perhaps to 

 centuries, during which the ice-cap was slowly forcing its way over the low-land, 

 and out to sea over a long extent of gentle slope, until it reached a depth con- 

 siderably beyond 200 fathoms, when the lower specific weight of the ice caused an 

 upward strain which at length overcame the cohesion of the mass, and portions 

 were rent off and floated away. The icebergs when they are first dispersed float 

 in from 200 to 250 fathoms ; when, therefore, they have been drifted to latitudes 

 of 65° or 04° south, the bottom of the berg, the surface which forced itself glacier- 



