GEOLOGY. 283 



ellers who visit Naples feel an interest in seeing it. Unfortunately, 

 like some other grottos, its enchantment disappears on a near view. It 

 is a little hole dug artificially into the foot of a hill facing Lake Agnano. 

 The aperture is closed by a door, and the space within is barely suffi- 

 cient for one person to stand erect. Into this narrow cell a poor little 

 dog is very unwillingly dragged, and placed in a depression of the 

 floor, where he is soon narcotized by the carbonic acid. The earth is 

 warm to the hand, and the volume of gas given out is very constant. 

 Such is the world-renowned Grotto del Cane, which, if it did not equal 

 our anticipation, at least afforded us the opportunity of some merri- 

 ment. Prof. Silliman's Notes on Europe. 



THE SALT LAKE OF UTAH. 



LIEUT. GUXNISON", of the Topographical Engineers, who has been em- 

 ployed for some time past in the survey of the great basin in which 

 the Salt Lake is situated, speaks of the lake as an object of the greatest 

 curiosity. The water is about one third salt, yielding that amount on 

 boiling. Its density is considerably greater than that of the Dead Sea. 

 One can hardly get his whole body below the surface. In a sitting 

 position, the head and shoulders will remain above water, such is the 

 strength of the brine, and, on coming to the shore, the body is covered 

 over with an incrustation of salt, in fine crystals. The most surprising 

 thing about it is the fact, that during the summer season the lake throws 

 on shore abundance of salt, while in the winter season it throws up 

 glauber salt in large quantities. The reason of this is left to the scien- 

 tific to judge, and. also, what becomes of the enormous amount of fresh 

 water poured into it by three or four large rivers Jordan, Bear, and 

 Weber as there is no visible outlet. 



ON EARTHQUAKES. 



MR. MALLET, at the British Association, presented some additional 

 observations on the limits of earthquake waves.* The rate of transit 

 was expected to be the least rapid in sand, and most in some elastic, 

 homogeneous, crystalline rock. Accordingly, a mile was measured on 

 the sands near Dublin, and a cask of powder buried at one extremity ; 

 the interval between the firing of the powder and the indication of 

 the shock at the other station, as registered by Wheatstone's chrono- 

 graph, gave a rate of 965 feet per second as the average of ten good 

 experiments. A shorter base was measured on the granite, and shocks 

 produced by borings three and a half inches diameter, and eighteen 

 feet deep, in which as much as twenty pounds of powder exploded. 

 The experiment was repeated twenty or thirty times ; and where the 

 granite was most shattered the shock arrived at the rate of only 1,299 

 feet per second ; under the most favorable circumstances, where the rock 

 was most homogeneous, the impulse travelled at 1,661 feet per second. 

 In many of the most celebrated earthquakes, clocks have been stopped, 



* See Annual of Scientific Discovery, 1851, p. 273. 



