238 A NATURALIST ON THE "CHALLENGER." 



the effects of growth of the base of a berg during one winter 

 when it probably still lay far south. The surface water would 

 be colder then, and the cliffs not being so much, or hardly 

 at all undermined, time would be allowed for the rising without 

 destruction of the platform, and thus the process need not be so 

 sudden. 



At first sight it seemed to me easy enough that the berg 

 should rise suddenly by the falling of part of its mass, but on 

 considering the matter with a plan showing the vast proportion 

 of its bulk required to be thus removed, I found the question 

 more difficult. 



The height of the main cliffs of the bi-tabular berg figured was 

 estimated by Captain Tizard at about 200 feet, and that of the 

 lower cliffs at 60 feet. We saw some distant bergs which were 

 possibly 300 or 400 feet in height and three or four miles 

 in length. A berg 200 feet in height would have a base extend- 

 ing to a depth of 300 fathoms or so, according to its form, and 

 this base will be thawed at different rates at successive depths, 

 according to the distribution of temperature in the water at the 

 various depths. The shapes of the bergs below water must 

 thus follow curves corresponding to those used by physicists to 

 express successive deep-sea temperatures graphically. 



A very large proportion of the bergs seen by us were as thus 

 described, flat topped and maintained their original balance. 

 Very many were bounded by a single range of cliffs washed by 

 the waves all round. In some these ranges were evidently old 

 and very much indented. These are simple bergs (see the 

 coloured plate, fig. 4.) 



Many were highly complex, combining two stories, lines of 

 caves, talus slopes, and evidences of having tilted to a certain 

 angle from the original line of flotation once or twice ; some 

 were excessively worn and weathered, having apparently been 

 long in warmer regions, and were pinnacled and broken up 

 by deep gullies or channels bounded often by rounded ridges 

 projecting at their mouths on either side. 



One much weathered pinnacled berg was passed which had 

 its entire surface shining and polished as if it had recently 

 toppled, and no fresh snow had fallen since this had occurred. 



