Formation of icebergs. 

 Separation from the land. 



ANTARCTIC CRUISE. 



Boulders in icebergs. 



147 



ward of that line, which is no doubt owing to the 

 situation of the land. From the great quantities of 

 ice to .be found drifting in all parts of the ocean in 

 high southern latitudes, I am induced to believe 

 that the formation of the ice-islands is much moi-e 

 rapid than is generally supposed. The manner of 

 their formation claimed much of my attention 

 while among them, and I think it may be explained 

 satisfactorily and without difficulty. In the first 

 place, I conceive that ice requires a nucleus, 

 whereon the fogs, snow, and rain, may congeal and 

 accumulate ; this the hind affords. Accident then 

 separates part of this mass of ice from the land, 

 when it drifts off, and is broken into many pieces, 

 and part of this may again join that which is in 

 process of formation. 



From the accumulation of snow, such a mass 

 speedily assumes a flat or table-topped shape, and 

 continues to increase. As these layers accumulate, 

 the field-ice begins to sink, each storm (there of 

 frequent occurrence) tending to give it more 

 weight. The part which is now attached to the 

 land remains aground, whilst that which is more 

 remote being in deep water is free to sink. The 

 accumulated weight on its outer edge produces fis- 

 sures or fractures at the point where it takes the 

 ground, which the frosts increase ; thus separated, 

 the surface again becomes horizontal, and continues 

 to receive new layers from snow, rain, and even 

 fogs, being still retained to the parent mass by the 

 force of attraction. The fogs have no small in- 

 fluence in contributing to the accumulation : some 

 idea may be formed of the increase from this cause, 

 from the fact that during a few hours the ice accu- 

 mulated to the thickness of a quarter of an inch on 

 our rigging and spars, though neither rain nor 

 snow fell. It may, therefore, I think, be safely 

 asserted that these icebergs are at all times on the 

 increase ; for there are few days, according to our 

 experience in this climate, in which some mode of 

 precipitation does not prevail in these high lati- 

 tudes, where, according to our observations, ice 

 seldom melts. The temperature of even the sum- 

 mer months being rarely above the freezing point, 

 masses of a thousand feet in thickness might re- 

 quire but few years to form. Icebergs were seen 

 in all stages of formation, from five to two hundred 

 feet above the surface, and each exposed its strati- 

 fication in horizontal layers from six inches to four 

 feet in thickness. When the icebergs are fully 

 formed, they have a tabular and stratified appear- 

 ance, and are perfectly wall-sided, varying from 

 one hundred and eighty to two hundred and ten 

 feet in height. These were frequently found by 

 us in their original situation, attached to the land, 

 and having the horizontal stratification distinctly 

 visible. 



In some places we sailed for more than fifty 

 miles together, along a straight and perpendicular 

 wall, from one hundred and fifty to two hundred 

 feet in height, with the land behind it. The ice- 

 bergs found along the coast afloat were from a 

 quarter of a mile to five miles in length ; their 

 separation from the land may be effected by severe 

 frost rending them asunder, after which the violent 

 and frequent storms may be considered a sufficient 

 cause to overcome the attraction which holds them 

 to the parent mass. In their next stage they ex- 

 hibit the process of decay, being found fifty or 

 sixty miles from the land, and for the most part 



with their surfaces inclined at a considerable angle 

 to the horizon. This is caused by a change in the 

 position of the centre of gravity, arising from the 

 abrading action of the waves. 



By our observations on the temperature of the 

 sea, it is evident that these ice-islands can be little 

 changed by the melting process before they reach 

 the latitude of 60. The temperature of the sea (:\s 

 observed by the vessels going to and returning 

 from the south), showed but little change above 

 this latitude, and no doubt it was at its maximum, 

 as it was then the height of the summer season. 



During their drift to the northward, on reaching 

 lower latitudes, and as their distance from the land 

 increases, they are found in all stages of decay ; 

 some forming obelisks ; others towers and Gothic 

 arches ; and all more or less perforated : some 

 exhibit lofty columns, with a natural bridge resting 

 on them of a lightness and beauty inconceivable in 

 any other material. 



While in this state, they rarely exhibit any 

 signs of stratification, and some appear to be 

 formed of a soft and porous ice ; others are quite 

 blue ; others again show a green tint, and are 

 of hard flinty ice. Large ice-islands are seen that 

 retain their tabular tops nearly entire until they 

 reach a low latitude, when their dissolution rapidly 

 ensues ; whilst some have lost all resemblance to 

 their original formation, and had evidently been 

 overturned. The process of actually rending asun- 

 der was not witnessed by any of the vessels, 

 although in the Flying-Fish, when during fogs 

 they were in close proximity to large ice-islands, 

 they inferred'from the loud crashing, and the sud- 

 den splashing of the sea on her, that such occur- 

 rences had taken place. As the bergs gradually 

 become worn by the abrasion of the sea, they in 

 many cases form large overhanging shelves, about 

 two or three feet above the water, extending out 

 ten or twelve feet ; the under part of this project- 

 ing mass exhibits the appearance of a collection of 

 icicles hanging from it. The temperature of the 

 water when among the icebergs, was found below 

 or about the freezing point. 



I have before spoken of the boulders embedded 

 in the icebergs. All those that I had an oppor- 

 tunity of observing, apparently formed a part of the 

 nucleus, and were surrounded by extremely com- 

 pact ice, so that they appear to be connected with 

 that portion of the ice that would be the last to 

 dissolve, and these boulders would therefore in all 

 probability be carried to the farthest extent of 

 their range before they were let loose or deposited. 



The ice-islands, on being detached from their 

 original place of formation by some violent storm, 

 are conveyed to the westward by the south-east 

 winds which are prevalent here, and are found, the 

 first season after their separation, about seventy 

 miles north of the barrier. This was inferred from 

 the observations of both the Vincennes and Por- 

 poise, the greatest number having been found about 

 that distance from the barrier. That these were 

 recently detached is proved by their stratified ap- 

 pearance ; while those at a greater distance had 

 lost their primitive form, were much worn, and 

 showed many more signs of decay. Near the 

 extreme point of the barrier visited, in longitude 

 97 E., latitude 62 30' S., and where it begins to 

 trend to the westward, vast collections of these 

 islands were encountered. From this point they 



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