GEOLOGY. 249 



FORMATION OF FRESH-WATER PONDS ON THE COAST. 



AT one of the meetings of the Boston Natural History Society, 

 Dr. Cabot stated, that, during a recent visit to the east end of Long 

 Island, he had made some interesting observations on the formation of 

 the fresh-water ponds by the closing up of the entrances to inlets from 

 the sea. He mentioned one, which is from four to six miles in circum- 

 ference, and separated from the sea by a sand-beach about twenty rods 

 wide. Within the memory of those now living it was an open strait, 

 but its waters are now entirely fresh, and contain fresh-water animals 

 and plants. Within twenty years oysters could be obtained here, and 

 their shells are still abundant. In the same vicinity are many other 

 similar ponds, and in many cases the process may now be seen going on. 

 The sea washes up a sand-bar across a bay, and in time stops the en- 

 trance. It is an interesting question, how the water in these ponds be- 

 comes changed from salt to fresh. 



This statement gave rise to some discussion in the course of which it 

 was remarked, that the change in the water might, perhaps, be accounted 

 for by supposing that all the water originally inclosed had percolated 

 through the sandy bottom, and its place had been supplied by rains and 

 neighbouring springs. 



ICE-CAVE IN RUSSIA. 



IN the recent work of Sir R. I. Murchison on the Geology of Russia, 

 he mentions a remarkable ice-cave, situated not far from Orenburg. 

 It is at the base of a hillock of gypsum, at the eastern end of a village 

 connected with the imperial establishment, and is one of a series of 

 apparently natural hollow T s used by the peasants for cellars or stores. 

 It possesses the remarkable property of being partly filled with ice in 

 the summer, and totally destitute thereof in winter. 



" Standing," says the author, " on the heated ground, and under a 

 broiling sun, I shall never forget my astonishment, when the woman to 

 whom 'the cavern belonged opened a frail door, and a volume of air so 

 piercingly keen struck the legs and feet, that we were glad to rush into 

 a cold bath in front of us to equalize the effect ! We afterwards sub- 

 jected the whole body to the cooling process by entering the cave, 

 which is on a level with the street. At three or four paces from the 

 door, on which shone the glaring sun, we were surrounded by half- 

 frozen quass and the provisions of the natives. The roof of the cavern 

 hung with solid undripping icicles, and the floor might be called a sta- 

 lagmite of ice and frozen earth. We were glad to escape in a few mi- 

 nutes from this ice-bound prison, so long had our frames been accustom- 

 ed to a powerful heat." The cold in this cavern is invariably the greatest 

 inside when the air is the hottest outside. As soon as winter sets in 

 the ice disappears, and in mid-winter the peasants assured the travellers 

 that the cave was of so genial a temperature, that they could sleep in 

 it without their sheepskins. At the very period when Sir R. I. Mur- 

 chison visited it, the thermometer was 90 degrees in the shade ; yet 

 a single plank was the division between a burning sun and a freezing 



