DRIFT DIVISION. 
227 
rock, and to float them off to distant parts. Ground ice, if formed in thick masses and moved 
by the currents, would afford an explanation of most of the phenomena of transport of the 
drift, and of scratches ; but it would not explain the elevations and depressions of drift, unless 
floated along beneath the surface, or in masses of very great thickness. On this point we 
have no direct evidence. The phenomena of ground ice are worthy of investigation. It is by 
means of this ice only that all the phenomena of the drift can be reconciled, as far as we 
know at the present time.* This would seem to imply a temporary change of climate at the 
drift period ; for ground ice is not, so far as we know, formed abundantly, as we might sup¬ 
pose it to have been in many places in southern New-York, where we have undeniable evi¬ 
dence that erratics from varied altitudes have been transported many miles. 
It has been shown from physical considerations that the earth is contracting in diameter, 
and consequently increasing in its velocity of rotation, either steadily or paroxysmally, probably 
both. A sudden yielding of the crust, would produce a sudden acceleration of rotation, and 
a sudden acceleration of the great equilibrating currents of the ocean; and such an occur¬ 
rence, when our country was mostly beneath the ocean, would tend to cause vast quantities of 
ice to be transported from the polar regions to those parts where we find the erratics. This 
ice would have a tendency to alter the mean temperature of the climate under its influence, 
rendering it colder, and sufficient, it is believed, to account for the phenomena of local drift, 
by means of local surface ice and ground ice. 
It is probable that a sudden acceleration of the velocity of rotation of the earth, so small as 
to be scarcely capable of measurement, except by long continued observation by astronomers. 
* Sand is frequently found cemented by ice in cold weather, in rivers. Gravel, earth, and mud, have been found in ice 
floated to the shore, that has risen from the bottom. The spiculae of ice, by a polarity under certain circumstances, be¬ 
come aggregated rapidly into great masses. Fishermen have often observed such facts; and frequently, in frosty weather, 
their anchors drag over the smooth icy bottom. The anchors when raised are sometimes coated with ice; and it some¬ 
times forms on them in such quantities as to raise them to the surface by its buoyancy. Ice is frequently raised by them, 
instead of fish on their hooks. Sluices and flood-gates are often rendered immovable by ice formed at the bottom. Ground 
ice often attains a great thickness before it rises to the surface, and raises by its buoyancy not only stones, earth and 
gravel, but large rocks. In the River Elbe, the rocks to which buoys have been attached on shoals, have been raised by 
the ground ice, and floated to other parts of the river. 
M. Brauns, after consulting with much care the best sources of information, learned that in the northern seas, both 
the ground ice and the grain ice (which rises in grains like hail to the surface) were found where the depth of water was 
one hundred and eight feet. In the Baltic sea, the ground ice was found at depths still greater. Some additional obser¬ 
vations have been made in England, by Mr. Knight. 
Vide Phil. Trans. London, 1816; and Mr. Mease, Edinburgh Encyclopaedia, Phil. Vol. 11, p. 70. 
Vide also, on ice, 
Demarest, Journal de Physique, Jan. 1783; 
Hassenfratz, Id. Jan. 1785; 
D’Antic, Id. Jan. 1788; 
M. Jules-Henri Pott, Id. July 1788; 
M. Hericaut de Thury, Journal des Mines, 1813, Vol. 33, p. 157. 
ScoRESBY, in the Memoirs of the Wernerian Nat. His. Soc. of Ed. Vol. 2, part 2. 
Col. Beaufoy, in Thomson’s Annals, May, 1817. 
