formation at a period equally remote with that of the origin of some of 
our tertiary rocks.* They are of the same nature as the glaciers of the 
warmer regions of the earth ; but instead of being melted in the valleys, 
they are pressed forward into the ocean till at length the water is sufficient 
to float them, and immense blocks are broken off. This process has been 
termed by the Greenland whale fishermen, the “ calving” of an iceberg. 
Drift ice, and all the other varieties of field ice, not only have a 
more recent origin, hut they are of a less enduring character when 
drifted into the warmer climates. When carefully examined they are found 
to consist of crystals of ice and crystals of marine salts, aggregated to- 
gether, the salt being separated from the water by the process of freezing. 
It is a well-known fact, that when small particles of ice and salt are 
mingled together, they will dissolve at a much lower temperature than that 
at which ice will dissolve ; consequently icebergs are found at a much lower 
latitude than drift ice. Generally drift ice is not to be met with in the 
southern oceans at a lower latitude than 58°, and, in that region, only in 
the Austral winter months from April to September inclusive. In one 
region, to which I shall more particularly refer, it has been found as low as 
55°, and in some cases brash ice has been reported in lower latitudes* But 
in these last instances, from the numerous icebergs adjacent, and from the very 
irregular sizes and forms of the ice, I am inclined to believe that it con- 
sisted of the debris of icebergs, and was not brash ice properly so called.f 
In the northern hemisphere, icebergs do not appear to attain the dimcn- 
* In tlie northern hemisphere they have their principal birthplace on the coast of 
Spitzbergen and the eastern shores of Greenland. The Altai mountain range gives rise 
to glaciers similar to those of Switzerland. But the cold of Siberia is not sufficiently 
intense to allow these glaciers to become icebergs. There they are gradually dissolved 
by the summer’s sun, and feed with their waters the rivers Kutania and Lena. Still, 
however, immense blocks of ice are brought down from the glaciers to the coast by 
these rivers ; although they cannot be denominated icebergs, they possess a common, 
origin. In 1799 a Tungusian discovered in one of them the body of a Mammoth, 
an extinct species of mammal, the fossil remains of which are found in the deposits of 
the Pliocene period of Lyell. Now since it is a law that the progress of glaciers is slow 
in proportion to the low temperature of the climate, we cannot imagine that icebergs of 
the south owe their origin to a more recent period than block ice on the Siberian rivers ; 
consequently we may regard them as possessing a preadamite existence. 
f The only report of an ice field in the Southern Hemisphere that I have received 
wus that of one that was seen in the mouth of September, 1854, in lat. 58° S., long. 
50° W. 
