CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
295 
As soon as a piece of ice of this kind attains a certain size, it is detached from the 
ground and raised to the surface by the greater specific gravity of the water ; these 
masses, containing a quantity of gravel and weeds, unite and consolidate, and in a few 
hours the river becomes passable in sledges instead of in boats” (p. 202). 
These, and similar observations made in northern America, establish the efficacy of ice 
in transporting no inconsiderable quantity of shingle along the beds of rivers, and show 
that it tends both to shift the shoals and to deepen the channels. The conditions of the 
old postpliocene rivers were precisely such as to favour this formation of ground-ice ; for, 
without exception, the old alluviums are composed of coarse subangular shingle with 
but little sand, and very rarely with any subordinate seams of clay. 
These two agents, floods and ground-ice, would affect chiefly the river-channel. 
There is another agency which would co-operate in that direction, but would affect more 
especially the banks and shores of the river ; that is, the freezing of the ground and the 
rending of rocks by great cold. The power of this agent is well known ; I will there- 
fore confine myself to a few observations bearing upon our particular case. Crantz 
speaks of the talus of debris at the foot of the hills in Greenland as looking “ like a 
demolished city,” and says that some of “ the lesser hills or ledges of rock are still more 
subject to breaking, and many of them grow so rotten and brittle with age that they are 
pulverized by the air”* * * § . Sir John B iCHARDSONf says that near Cape Krusenstern “ the 
whole surface is covered with thin pieces of limestone.” “ I should infer that the 
frost splits off the layers and breaks them up more effectively than any agent to 
which rocks are exposed in warmer climates.” The same thing occurs at Point Keats ; 
whilst of the limestone cliffs on Lake Winipeg he says, “ Under the action of frost 
the thin horizontal beds of this stone split up, crevices are formed, perpendicularly, large 
blocks are detached, and the cliff is rapidly overthrown, soon becoming masked by its own 
ruins. In a season or two the slabs break into small fragments,” which go to form the 
beach. 
Dr. Sutherland $, in describing the effects of a still colder climate, with reference to 
the great talus generally found at the base of the cliffs in the Arctic regions says, 
“ Strong and bold as this coast may appear to be, and bidding defiance to assault in all 
directions, time, with its invisible agent, heat alternating with cold, assisted only by 
water, saps its foundations, and runs mines into its lofty citadels ; and the result of this 
action is an increasing heap of rubbish, upon which the same agents are still exerting 
their irresistible power, reducing to splinters and small fragments, and ultimately to a 
fine powder, liable to be washed or blown into the sea, what had been set free in masses 
of more than a ton weight.” 
In Siberia the same phenomenon is often alluded to by Baron Wrangell §. 
* History of Greenland, vol. i. p. 53 : London, 1767. 
t Searching Expedition, vol. i. pp. 295, 281, & 65. 
£ Journal of a Yoyage in Baffin’s Bay and Barrow Straits, vol. i. p. 286 : London, 1852. 
§ Op. tit. pp. 193, 374. 
2 s 
MDCCCLXIV. 
