Natural History, 365 



of Basle, from which the following abstract has been made. 

 Ground ice is a name given to those detached and separated 

 masses which running waters carry on their surface during a 

 frost of some continuance. This ice differs from that which 

 forms xiontinuously along the banks of rivers, and particularly 

 in places where the water is tranquil. It never forms on lakes, 

 ponds, or stagnant waters, and motion appears essential to its 

 production. It appears to resemble a floating aggregation of 

 snow penetrated by water rather than common ice, but a more 

 attentive examination shews that it possesses peculiar characters. 

 It is, in fact, formed of an immense assemblage of small round 

 discs of thin ice, similar to each other, and each some lines in 

 diameter ; each disc is perfectly transparent, though when con- 

 glomerated, the whole presents the apjjearance of a semi-trans- 

 parent mass of wet snow. 



It is well known, that before this ice will appear on streams 

 and rivers, the temperature of the atmosphere must have been 

 retained for some time several degrees below 32°, and it is gene- 

 rally observed that a cold wind blowing in an opposite direction 

 to the course of the stream singularly favours the formation of 

 this kind of ice, which, fcr this reason, will, in rivers of the same 

 country, appear first on that flowing against the wind. 



Although it may be supposed that in consequence of the su- 

 perior levity of water at 32° above that which is a little 

 warmer, the particular ice in question is formed at the surface of 

 the water, yet it is to be remembered, that reasoning which ap- 

 plies correctly to standing waters, does not apply to rapid streams ; 

 and, as the name announces, ground ice really forms on the 

 earth constituting the bed of the river, and there are few water- 

 men or fishermen who cannot cite numerous cases of which they 

 were eye-witnesses, having seen masses rise from the bottom to 

 the surface, even from rivers of considerable depth. 



In the winter of 1S23, the canal of St. Alban, which conducts 

 the waters of the river to Basle, bore a considerable quantity of 

 gi-ound ice. The transparency of the water was such as to allow 

 of objects being seen three feet in depth. The bed of the canal 

 at that part is covered by round pebbles. Wherever at the bot- 

 tom of the water a projection occurred, either in deep or shallow 

 parts, morsels of ice, in bundles, could be discovered, which, at a 

 distance, appeared as collections of cotton flocks. In many 

 places, the bottom was almost covered by similar flocks, which 

 separated from time to time, and came to the surface of the 

 stream, here very rapid. Tiiese flocks, when taken from the 

 bottom, had exactly the same appearance as the ground ice which 

 floated in abundance on the surface, and were composed, like 

 it, of small plates of ice, rounded and agglomerated, so that 

 no doubt could exist as to the similarity of origin. The parti-- 



