CONTAINING FLINT IMPLEMENTS, AND ON THE LOESS. 
tion, however, to the ice so formed, observations of late years have shown that a very 
considerable formation of ice takes place along the beds of certain rivers, especially 
when those beds are stony and gravelly. In these climates we rarely have the opportunity 
of observing this phenomenon on a large scale, although, from a few facts noticed, it 
appears even here to be far more common than has been supposed. 
That this agent is one of considerable power in producing changes of the character 
we are referring to, is evident from the facts recorded by Arago *, and the experiments 
made by M. Leclercq f at Liege, and by Colonel Jackson in Russia. These observers 
show that most running streams give rise, under certain conditions, on the setting in of 
winter, to the formation of ground-ice. In the first place the whole body of water be- 
comes reduced, by intermixture caused by the flow of the river, to a uniform temperature 
of 32°. Any pointed surfaces in the bed of the river then determine, as is the case with 
a saturated saline solution, a sort of crystallization, needles of ice being formed, which 
gradually extend from point to point and envelope the substances with which they are 
in contact. By this means the whole surface of a gravelly river-bed may become coated 
with ice, which on a change of temperature, or of atmospheric pressure, or on acquiring 
certain dimensions, rises to the surface, bringing with it all the loose materials to 
which it adhered. 
According to M. Leclercq, whose observations were made in the winters of 1840 and 
1841, when the mean temperature of the end of December was 12° Fahr., ground-ice is 
formed in a current of 3 - 60 feet per second on the fifth day; and with a current of 9 '52 
feet to 11*58 feet, on the ninth to the eleventh day. The greatest depth at which he 
observed the formation of ground-ice was not quite 4 feet, and the greatest thickness the 
ice attained was 2 '63 feet. At one time he found the river-bed, for a length of a mile, 
covered with lumps of ice, “ which became detached from time to time, in angular 
masses of a metre square, and carried away pebbles and stones, which after a time 
became detached and fell on the beds over which they were carried.” The conclusions 
at which M. Leclercq arrived were — 
“ 1st. That the ice is formed under water so much the more as the cold is the more 
intense and the sky is the clearer.” “ 2nd. That the ice under water gains in thickness 
so much the more as the current is less swift.” 
He also observed that a bed of fine clay and gravel gave rise to no ice, and that “ the 
bed best suited to produce it was one formed of pebbles of considerable size.” 
Colonel Jackson % experimented on the Neva, which at St. Petersburg is about 1500 
feet broad and in places 50 feet deep, and moves with a velocity of about 2-g- miles per 
hour. It is frozen during five months in the winter, and the surface-ice attains a thick- 
* “ Sur les glagons que les rivieres charrient en hiver,” Annuaire du Bureau des Longitudes pour 1833, p. 244. 
t “ Sur la formation de la glace dans les eaux courantes,” Mem. couronnes par l’Acad. de Bruxelles, t. xviii. 
1845. 
+ “ On the Congelation of the Neva at St. Petersburg, and Temperature of its waters when covered by ice,” 
Journal of the Boyal Geographical Society, pp. 2, 7 13, vol. v. 1835. 
