GEOLOGY. 305 



and simple combustibles, some of which, as titanium or boron, com- 

 bine with it directly with such avidity that the union is attended with 

 combustion, and has also proved that the nitrides formed are decom- 

 posed by the hydrated alkalies, ammonia being thereby generated, 

 it had occurred to the author that a more probable explanation of the 

 occurrence of ammonia in volcanoes might be afforded by supposing 

 such combinations to take place in the interior of the earth, and to be 

 subsequently decomposed by the alkalies which are usually present 

 wherever volcanic action is taking place. In confirmation of this 

 view, he appealed to a late observation made at Naples, -namely, that 

 metallic titanium had been found evolved from the crater of Vesuvius, 

 during a late eruption. 



EARTHQUAKES AND VOLCANIC ERUPTIONS FOE 1861. 



The most serious earthquake of the year occurred in the night of the 

 20th of March, overwhelming the city of Mendoza, in the Argentine 

 Republic, South America. Mendoza is in lat. 32 53' S., Ion. G9 6' 

 \V., and is about 2900 feet above the sea on the eastern slope of the 

 Andes. The shock is said to have come from the north, followed by 

 another from the south, and to have lasted only about five seconds, in 

 which brief time nearly the whole town was utterly laid waste, and 

 from 8000 to 12,000 lives were destroyed. Travellers among the 

 Andes, in the district affected by the earthquake, describe the scene 

 as awful: deep caverns were opened into the bowels of the moun- 

 tains, the mountain summits parted asunder, and the earth in many 

 places burst open like a bomb-shell, ejecting water and enormous 

 stones. 



The most important volcanic eruption of the year took place in 

 an unusual locality, viz., on the east coast of Africa, on the 7th of 

 May, from a heretofore unrecognized volcano at Djebel Dubbeh, situ- 

 ated in about 13 57' N. lat., and 41 20' E. long. It was accom- 

 panied by loud shocks, resembling the discharge of artillery, and im- 

 mense clouds of dust. The noises were distinctly heard at places 

 nearly 400 miles apart, and the dust fell for several days over a vast 

 extent of the Red Sea, and on the coast of Arabia. At Edcl, on the 

 Abyssinian coast, a day's journey from Djebel Dubbeh, the dust was 

 knee-deep, and its fall during the first day caused total darkness. 

 The eruption continued at intervals for three or four days. There is 

 no remembrance of any previous eruption. 



Vesuvius has also been extremely active during the past year. 



GEOLOGICAL SUMMARY. 



Origin of Granite. Interesting results of a microscopic examina- 

 tion of granite have recently been published by Mr. Sortby, F. R. S., 

 of England. It appears that by reducing granite by grinding and 

 polishing to extremely thin films, so as to render them transparent, 

 like gold leaves, Mr. Sortby has discovered that this rock contains a 

 large number of cells or cavities holding water or saline solutions ; 

 hence it may be inferred, to the great satisfaction of the Neptunians. 

 that granite waAiot solely produced by the action of fire, but that 

 water had a great deal to do with it. 

 26* 



