Geological Society of London. 285 



waves behave towards more or less incolierent deposits reposing on 

 inclined or on level beds, under various conditions. 



Mr. Mallet also explained the dynamic conditions under which the 

 water from water-bearing beds, such as that of ooze beneath the 

 Cachar clay-beds, becomes elevated in the fissures formed, and gave 

 approximate expressions for the minimum height to which the water 

 can rise in relation to the velocity of the elastic wave particle. The 

 paper concluded with remarks upon the continual noises, like the 

 irregular fire of distant artillery, heard long after the shock had 

 passed, and when the country had become perfectly quiescent. 



Discussion. — Mr. Scott -wished to ascertain the author's opinion as to the 

 possibility of predicting earthquakes on meteorological grounds, as had been done 

 by M. Boulard, several of whose prophecies were said to have been fulfilled. 



Mr. D. Forbes gave some details of the earthquake of Mendoza, a town situated 

 on a vast alluvial plain at the foot of the Andes, in which the phenomena remark- 

 ably coincided with those detailed by Dr. Oldham. In that case he found that the 

 rumours as to fire and smoke having been emitted from fissures were entirely without 

 foundation, the presumed smoke having been nothing but dust. The earthquake 

 was felt over a distance of 1200 miles ; and wherever the firm rock came to the sur- 

 face there was no trace of fissure, though portions of the rock were overthrown. But 

 in the plain, consisting of 30 or 40 feet of alluvial soil, the whole ground was in 

 places fissured, and in some districts the surface completely furrowed, and even the 

 turf turned over. He had witnessed numerous earthquakes, and in some cases had 

 been in deep mines during their occurrence, when the sound only could be heard, and 

 he could testify to their effects being confined to the surface. The direction of 

 the fissures was invariably at right angles to the line of shock. In South America 

 all the earthquakes could be traced to volcanic centres. 



The President inquired as to the distinction to be drawn between the primary and 

 secondary efi'ects of earthquakes, and whether the author thought that no fissures 

 were attributable to the direct action of earthquakes ; also as to the cause of the sounds. 



Mr. Mallet, in reply, explained that fissiu-es only take place where masses were 

 comparatively free in one direction. They might extend to enormous depths, though 

 they often closed in rapidly. With regard to the power of predicting earthquakes, 

 he disbelieved in it wholly, and considered that any fulfilment of such prophecies 

 must be due to accident; earthquakes are so numerous, that the chances of such 

 fulfilments are great. The blow or impulse originating earthquakes could not be 

 attributed solely to one cause. It arose often from deep subterranean volcanic action, 

 but it also — especially in the case of long-continued tremors, like those of Comrie or 

 Pignerol — arose from the breaking up or the grinding over each other of rocky beds 

 at a great depth, through the tangential pressures produced in the earth's crust by 

 secular cooling. The arrested impulse of the fall of the Rosberg in Switzerland 

 produced a sensible earthquake. Fissures in hard rock could not he produced 

 directly by the shock, because the velocity of impulse in such rock greatly exceeded 

 that of the elastic wave particle. The earth's crust was at present not in a state of 

 tension, but of compression, through secular cooling. 



III.— April 24, 1872.— Prof Eamsay, F.E.S., Y.P., in the Chair.— 

 1. " An extract from a despatch from H.M. Minister in Teheran." 

 From the Eight Hon. the Earl Granville, Secretary of State for 

 Foreign Affairs. It described the effects of some severe earthquake 

 shocks experienced at Khabooshan, in North- Western Khorassan. 

 On the 23rd December, 1871, an earthquake occurred, which destroyed 

 half the town of Khabooshan, and buried about 2000 of its inhabitants 

 in the ruins. On the 6th January, 1872, another severe shock de- 

 stroyed the remainder of the town, and killed about 4000 people. 

 Four forts near the town were so completely buried that not a trace 

 of them can be seen. It was estimated that 30,000 lives were lost 



