I20 



NATURE 



[Dec. 7, 1876 



ON THE CONDITIONS OF THE ANTARCTIC^ 

 II. 



ALTHOUGH no land debris of any kind was observed 

 by us on the icebergs, there cannot be the slightest 

 doubt that such is carried by them all over the region and 

 distributed on the bottom. The samples brought up by the 

 sounding instrument consist almost entirely of commi- 

 nuted clays and sands, and the dredge always contained 

 in considerable quantity, about the meridian of 8o* E., 

 chiefly basaltic pebbles, and, further to the eastward, 

 pebbles and larger fragments of metamorphic rocks, 

 granite, gneiss, mica-slate, hornblende-slate, clay-slate, 

 and chlorite-slate. 



While the evidence may be said to be conclusive that 

 these icebergs have their origin on land, it seems to me 

 that the presumption is greatly in favour of the land at 

 their breeding-place having been comparatively low and 

 flat, and bordered for a considerable distance by shoal 

 water. Although the white ice which forms the exposed 

 portion of the flat-topped southern icebergs is very hard, 

 its specific weight is considerably below that of abso- 

 lutely compact ice. Allowing for this difference, and 

 supposing that one-seventh part of the ice is raised above 

 the water, supposing also that the berg is symmetrical in 

 form, which, from its appearance and probable mode of 

 origin is likely to be the case ; before it has 

 been subjected to the action of the sea, the 

 submerged portion would be 1,200 feet in 

 depth, the berg would float in water 200 

 fathoms deep, and the average thickness - 

 of the land ice-cap would be 1,400 feet. ^ 

 From the comparatively small number of 

 icebergs at the point where we crossed the 

 Antarctic circle, and so far as we could 

 judge from our own observations and the 

 previous observations of others, for a con- 

 siderable distance to the west of the me- 

 ridian of 80° E., we were led to believe that 

 the place of their formation, the land and 

 the belt of shallow water girding it, was at 

 a very considerable distance from us. 



Although in the present state of our know- 

 ledge it would be rash to form any very de- 

 finite opinion as to the conditionsof the region 

 included within the parallel of 70° S., still 

 there are some indications which have a cer- 

 tain weight. We have no evidence that this space which 

 includes an area of about 4,500,000 square miles, nearly 

 double that of Australia, is continuous land. The pre- 

 sumption would seem rather to be that it is, at all events, 

 greatly broken up, a large portion of it probably consist- 

 ing of groups of low islands united and combined by an 

 extension of the ice-sheet. One thing we know, that the 

 precipitation throughout the area is very great, and that 

 it is always in the form of snow, the thermometer never 

 rising, even in the height of summer, above the zero of 

 the centigrade scale. 



Various patches of Antarctic land are now' known with 

 certainty, most of them between the parallels of 65° and 

 70° S. ; most of these are comparatively low, their height, 

 including the thickness of their ice-covering, rarely ex- 

 ceeding 2,000 to 3,000 feet. The exceptions to this rule 

 are Ross's magnificent volcanic chain, stretching from 

 Balleny Island to a latitude of 78° S., and rising to a 

 height of 15,000 feet ; and a group of land between 55° 

 and 95° west longitude, including Peter the Great Island 

 and Alexander Land, discovered by Bellingshausen in 

 1821 ; Graham Land and Adelaide Island, by Biscoe, in 

 1832 ; and Louis PhiHppe Land, by D'Urville, in 1838. 



The remaining Antarctic land, including Adelie Land, 



« The svibstance of a lecture by Sir C. Wyville Thomson, K. R.S., delivered 

 in the City Hall, Glasgow, on November 23, under the airangements of the 

 Glasgow Science Lecture Association.! Continued fro-n p. io6. 



discovered independently by Dumont D'Urville, and 

 Lieut. Wilkes, in 1840, in long. 140° 2' 30", lat, 

 66° 45' S ; Clairie Land, discovered by the same naviga- 

 tors about 3° farther to the westward ; Sabrina Land, dis- 

 covered by Balleny, in 1839 5 ^i^d Kemp Land and 

 Enderby Land, discovered by Biscoe, in 1833, nowhere 

 rise to any great height. If we were justified in adding 

 the " strong appearances of land " reported by Lieut. 

 Wilkes, which would virtually connect Ringgold's Knoll 

 not far from the Balleny Islands, with a point in long. 

 106° 18' 42" E., lat. 65° 59' 40' S., by a continuous coast- 

 line of moderate height, the extent of land of this charac- 

 ter would be considerably increased. 



The geological structure of the Antarctic Land is almost 

 unknown. South Victoria is actively volcanic and consists 

 doubtless of the ordinary volcanic products. D'Urville's 

 party landed on Adelie Land and found rocks of gneiss. 

 Wilkes reports having landed on an iceberg, long. 

 106° 18' 42''', and finding "imbedded in it in places 

 bouMers, stones, gravel, sand, and mud or clay. The 

 larger specimens were of red sandstone and basalt." At 

 the same place Lieut. Ringgold found that " the icebergs 

 near at the time presented signs of having been detached 

 from land, being discoloured by sand and mud." From 

 one iceberg he procured several pieces of granite and of 

 red clay which had been frozen in. Beyond these ob-er- 



Fn. 3.— February 25, 1874. Lat. 63^ 49' S-, Long. 94° 51' E. 



vations, and our own on'the nature of the pebbles brought 

 up by the dredge, we have no information. 



That the area within the parallel of 70° S. is continu- 

 ously solid, that is to say, that it is either continuous land 

 or dismembered land fused into the continental form by 

 a continuous ice-sheet, I think there can be little doubt. 

 The local cases of abnormal distribution of temperature 

 which produce suci remarkable conditions of climate 

 even within the North Polar Sea exist in the southern 

 hemisphere only to a very slight degree ; and we know by 

 the absence of any well-defined local Antarctic return-cur- 

 rents comparable with the Labrador current, or the current 

 round the south of Spitzbergen, that the function of such 

 currents as the Gulf Stream in ameliorating the northern 

 climate, and breaking up the ice, and producing a circu- 

 lation even in the highest northern latitudes, is not in any 

 way represented in the south. 



In favour of the view that the area in question is broken 

 up, and not continuous land, two considerations appear 

 to me to be very suggestive. If we look at an ice-chart we 

 find that the sea is comparatively free from icebergs, and 

 that the deepest notches occur in the " Antarctic continent" 

 at three points, each a little to the eastward of south of 

 the great land-masses, and I have little doubt that the 

 explanation of this fact lately suggested by Dr. Neumayer 

 is the correct one. The great equatorial current impinging 

 upon the eastern coasts of the continents bifurcates upon 



•yer I 

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