PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 969 



left a gray cretaceous deposit of nearly a quarter of an inch, 

 which was supposed to have been emitted hy the volcano of Etna. 

 Colored snow, doubtless, is the result of a deposit of vegetable 

 origin. In the middle of the last century, M. de Saussure, so 

 celebrated for his Alpine and meteorological researches, discov- 

 ered a considerable qnantit}^ of red snow ou some of the high 

 mountains of the Alps. In 1778 he made an analysis of some 

 collected on Mount St. Bernard, and proved that the coloring 

 matter vras a vegetable substance, possibly the fariua of some 

 flower.. It is now known that the red color of snow is sometimes 

 due to a minute species of lichen. Capt. Ross, during his first 

 voyage to the Arctic regions in 1818, collected some of the color- 

 ing matter from the crimson clifls discovered near Cape York, ou 

 BufSn's Bay, and visited by Kane in July, 1855. Under the micro- 

 scope it Avas found to consist of particles like a very minute round 

 seed of a deep red color. Ou some of the particles a dark speck 

 was also seen. On his return to England, Capt. Ross placed sev- 

 eral bottles of specimens in the hands of Dr. Wollaston, who, after 

 an examination, stated that the red matter consisted of minute 

 globules, from one-thousandth to three-thousandth of an inch in 

 diameter. Their coat was colorless, and the redness belongfed 

 wholly to the contents, which seemed to be of an oily nature, and 

 not soluble in water. M. Thenard, M. de Candolle, Robert Brown 

 and others, have expressed their opinion as to the vegetable char- 

 acter of the deposit, but from what plant it was derived is not so 

 satisfactorily settled. We inay here add that in the Grisons, 

 France, there was, last winter, a fall of red snow, to the depth of 

 three inches, continuing for two hours. The phenomenon is said 

 to be due to the presence of a microscopic mushroom, the jj'^'otoc- 

 oceus nivalis. 



Ice a Preventive of Aeration. 

 The reading of one of the foregoing items, relating to ice in fish 

 ponds, reminded Dr. Vanderweyde of a curious effect of ice pre- 

 venting the absorption of air by water. The city of Philadelphia 

 is supplied with water from the Schuylkill river, which is pumped 

 into an elevated reservoir. Some miles above the city are several 

 manufactories from which refuse matter is drained into the river. 

 For some distance the water is quite dark, ownng to the presence 

 of organic substances, but as it approaches the city it becomes 

 clearer — the oxygen of the air having been absorbed and the car- 



