206 AMONGST THE SOUTHERN ICE. 



rise should occur from the height of the old wash-line to the 

 present water-line, a mass of the berg above water must have 

 been suddenly removed, equal in volume to the whole part of 

 the berg above water lying below the level of the top of the 

 lower storey. 



It seems almost incredible that such a mass should break 

 off and fall away suddenly. A splitting in two can be 

 readily understood, but the mass in this case must come 

 entirely from the part of the berg above water. It cannot 

 have split off at an angle, for the walls of the berg in question 

 were perpendicular cliffs. The berg certainly had never 

 toppled. 



A different explanation possible is, that nine times the 

 volume of ice above referred to, was suddenly added to the 

 part of the berg below water by its passing into cold water or 

 a change of season. It may be that the raised storey represents 

 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 

 extending to a depth of 300 fathoms or so, according to its 

 form, and this base will be thawed at different rates at succes- 

 sive depths, according to the distribution of temperature in 

 the water at the various depths. The shapes of the ice 

 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. 



Many were highly complex, combining two stories, lines of 

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



