1870,] BROWN—PHYSICS OF ARCTIC ICE. 689 
vity it contains 52 oz. (avoird.) of salt to every gallon of 231 cubic 
inches, and freezes at 284 Fahr. The specific gravity of this ice is 
about 0:873. To enter upon this subject, of which the above is 
only the summary of a long series of experiments, is foreign to the 
object of this paper. From this bay-ice is formed the floe, from 
the floe the pack-ice and other forms familiar to arctic navigators. 
In the summer the ice in Davis Strait on either side breaks up 
sooner than that in the middle of the strait, which remains for a con- 
siderable time, forming the “middle ice” of the whalers. Still, 
however, a narrow belt remains attached to the shore during a con- 
siderable portion of the summer, ‘This is called by the Danes in 
Greenland the ‘iis fod,” and by the English navigators the “ ice- 
foot.” As the spring and summer thaws proceed, land-slips occur, 
and earth, gravel, and avalanches of stones come thundering down 
on the ice-foot, there to remain until it breaks off from the coast 
and floats out to sea with its raft-like load of land-débris. As the 
summer’s long sunlight goes on, the ice, worn by the sea, parts with 
its load; and this may be shortly after its leaving the land, or it may 
float tolerably far south. The ice-foot, however, rarely carries its 
load as far south as the mouth of Davis Strait; and sea-ice is seldom 
seen far out of the arctic regions, while, as we all know, bergs often 
float far into the Atlantic. Often fields of ice will float along and, 
like icebergs, graze the surface of rocks only a wash at low tides ; 
and therefore its action might be mistaken for that of icebergs or 
land-ice. In other cases I have known the ice-foot, laden with 
debris, to be driven up by the wind and high tides on to low-lying 
islands, spits, and shores, piling them with the load thus carried from 
distant localities, so that blocks of trap from the shores of Disco or 
Waygatz might be drifted up on the beach at Cumberland Sound or 
on the syenitic shores of South Greenland. 
It has even been found that in shallowish water the ice will freeze 
to the bottom of the sea; and in such situations the gravel, blocks, 
&e., there lying will freeze in and be carried out to sea, to be depo- 
sited in course of time in a manner similar to the superincumbent 
loads of the ice-foot, though more speedy. The same pheno- 
menon holds good of the Baltic. In the Sound, the Great Belt, cde. 
the ground-ice often rises to the surface laden with sand, gravel, 
stones, and sea-weed. Sheets of ice, with included boulders, are 
driven up on the coasts during storms and “ packed” to a height of 
50 feet. How easily such sheets of ice, with included sand, gravel, 
or boulders, may furrow and streak rocks beneath may be imagined’. 
The patches of gravel on the pack-ice are owing, I think, to portions 
of the gravel-laden ice-foot having got among the ordinary materials 
of the pack; for Ido not think that ice formed in deep water, unless 
when it passes over rocks, and therefore may take up fragments of 
stone or earth, has any geological significance. 
The conclusions which we are forced to draw from what I have 
said regarding the depositing-power of glacier-streams, bergs, and sea- 
ice must be:—1. That the bottom of Davis Strait must be composed 
1 Forchhammer in Lyell’s ‘ Principles,’ pp. 231-232. 
