2 
logical Institute; and of officials of our own Government, as well as 
those of the captains of Australian vessels to whom my appeal was 
addressed. Further, I have to acknowledge the services of several 
passengers, who have furnished me with sketches of icebergs, and the 
kindness of a lady-passenger on a homeward voyage of the “ Lightning/’ 
in drawing for me a beautiful sketch of an extraordinary iceberg, 420 
feet high ; this is also admirable as a work of art. I have also availed 
myself of information afforded in the published journals of Captains Cook 
and Furneaux, and other officers engaged in voyages of discovery, by 
which means I have been enabled to carry back my investigation to 1772. 
Ice of the Polar Seas may be divided into two classes — sheet ice and 
icebergs. These are quite distinct in their origin. Sheet ice is met with 
in different forms, which, however, are but various conditions of ice arising 
from a common origin, — in fact, the same ice is found at different times, 
under all the varied forms of ice-fields, ice-floes, pack, stream, drift and 
brash ice. All these are the result of one year’s frost, and the extent and 
depth of sheet ice depend generally on the intensity of the previous 
winter’s cold, and the circumstances connected with the succeeding season, 
which regulate the breaking up of the frozen surface. The return of the 
milder season gradually separates the ice into enormous fields, which are 
cast adrift on the ocean. Some of these in the Arctic region have been known 
to have an area of more than one hundred square miles. They vary from 
three to thirty feet in thickness. When broken into smaller sheets they are 
termed floes. When reduced to fragments crowded together they form what 
is termed pack ice ; this, when elongated, is called a stream ; and when 
further separated, it is known by the names of drift and brash ice, — the 
latter term being applied when the pieces have been ground down by abra- 
sion, or have lost all the characteristics of their original condition by the 
thawing action of a milder climate. Icebergs, however, differ altogether 
both in appearance and origin from the kinds of ice already described. 
Towering like precipices and pinnacles, varying from one hundred to a 
thousand feet above the surface of the sea, in some directions they assume the 
appearance of chalk cliffs, but near the edges of a fracture they exhibit in 
the sun a translucent appearance of emerald green. Between the spires 
and ridges at their summits are pools, and in some cases we may term them 
lakes, of azure blue. Icebergs are not the produce of one season ; on 
the contrary, there is reason to believe that these masses commenced their 
