GEOLOGY. 247 



descent of only 2 feet in the Danube presents the greatest obstacles to 

 navigation. It is obvious, therefore, that in treating of the fall of 

 rivers, their depth and width should also be taken into the account." 

 The River Dee, during the lust 72 miles of its course, falls 1,190 feet 

 or about 16^ feet to the mile, on an average; but it has not a single 

 waterfall or decided rapid. The Severn and the Shannon are much 

 alike in magnitude, but in a distance of 213 miles the latter descends 

 161 feet, while the former, in 210 miles, descends 465 feet, thus giv- 

 ing to the Shannon an average fall of 9 inches per mile, and to the 

 Severn one of 26 inches. Yet the Severn has no rapids or falls, 

 while the Shannon, with an average fall of one third less, forms some 

 magnificent rapids, which are the boast of Great Britain. Again, the 

 Tweed and Clyde are of about the same magnitude ; the former is 96 

 miles long, and its total fall is 1,500 feet; and the latter is 98 miles 

 long, with 1,400 feet of fall. At one point these two rivers are in the 

 same plain, and less than seven miles apart, yet the Tweed pursues 

 its course to the sea evenly and gently, while the Clyde has not 

 parted with its former companion for a greater distance than 18 miles, 

 before it dashes over falls whose total descent is 230 feet. Jamesoris 

 Journal, Oct. 



OCCURRENCE OF FRESH WATER OX BEACHES AND SANDY ISLANDS. 



MR. E. C. CABOT read a paper, giving an account of some researches 

 he had made, in company with Mr. Desor, to determine the fact of 

 the constant presence of fresh water in dune sand and sand-spits. 

 These researches were conducted at Cape Cod, which they visited in 

 the United States steamer Bibb, under the command of Lieut. Davis, 

 with whose assistance they were made. In every instance where 

 there was a body of sand above the tide-level, with salt water on 

 opposite sides, or entirely surrounding it, fresh water was discovered 

 on digging to a moderate depth. On the island of Monomoy, fresh 

 water was found at a depth of two feet. On the beach at the line of 

 high-water, it was obtained almost on the surface. The same fact 

 was observed on Sandy Neck, a long sand-peninsula, which separates 

 Barnstable Bay from Barnstable Harbour. This is particularly re- 

 markable, as good water is very scarce in the town of Barnstable, on 

 the main land directly opposite. In this town is a well, about 150 

 feet from the shore, in which the water rises and foils with the tide, 

 although only through a space of a foot and a half. As yet Mr. C. 

 had not been able to satisfy himself whether the amount of rise and 

 fall in wells showing this sympathy with tidal fluctuations, depends 

 upon their distance from the salt water or not. Since making these 

 observations, he had noticed that such a rise and fall is not limited to 

 w r ells in a natural formation. He had observed that, in loose deposits 

 of an artificial character, in the vicinity of salt-water, they also occur, 

 as he had seen in several of the new streets of Boston, \vhere at high 

 tide trenches were found to contain fresh water, but were empty at 

 low tide. An interesting inquiry suggests itself, as to the origin of 

 these deposits of fresh water in such loose soil. They cannot be 



