282 Geological Society. 



tion of a uucleus Trith respect to supersaturated saline solutioDS. If 

 the solid be made cliemicaliy clean, ir may be plunged into the solu- 

 tion without altering its tension, and hence there is no separation of 

 salt. And here it mav be remarked that such a case is possible as 

 that a crystal of the salt itself may be brought into contact with the 

 solution without disturbing its tension, and hence be inactive. It 

 has never been pretended that a crystal of the salt is not a good nu- 

 cleus for a supersaturated solution of its own kind ; all that has 

 been stated by one of us is that, under special conditions, such a 

 crvstal mav be lowered into the solution without actins: as a nucleus. 



GZOLOGICAL SOCIETY. 

 "Continued from p. I49.j 



April 10, 1-72.— His Cirace the Duke of Ai^gyU, K.T., I.E.S., 

 President, in the Cliair. 



The following commimication was read : — 



" Xo tiee of some of the Secondary Enects of the Earthquake of the 

 10th January. 1869, in Cachar."" Communicated by Dr. Oldham, of 

 Calcutta, with remarks by Eobert Mallet, Esq., C.E., E.E.S. 



This earthquake was a severe one, being strongly felt in Calcutta^ 

 distant firom the meizoseismic area about 200 miles, and far into 

 the plain, of "Bengal. 



The effects were examined on the spot a few weeks after the 

 shock by Dr. Oldham, who anticipates being able to fix the position 

 and depth of the centre of impulse by following the same methods 

 as those first employed by Mr. Mallet with respect to the ^ great 

 Xeapolitan earthquake of 1S57. 



These results have not yet been received ; but Dr. Oldham has 

 forwarded an extremely interesting letter on the circumstances of 

 production of very large earth-fissures, and of the weUing up of 

 water from these, derived from the water-bearing ooze-bed, upon 

 which reposed the deep clay-beds in which the fissures were formed. 



Dr. Oldham rightly views all these fissures, which were all nearly 

 parallel to and not far distant from the steep river-banks, as 

 " secondary effects,"" and not due to fractures produced by the direct 

 passage of the wave of shock. He also shows that the weUing up 

 or overflowing of the water in the fissures was a secondary efiect 

 also, and negatives the notion entertained on the spot of mud-vol- 

 canoes lire, having originated at those fissures. 



"The chief aim of ]«Ir. Mallet's remarks was to point out the 

 importance to geologists of rightly comprehending the dynamics of 

 production of these phenomena, and to show that the older notions 

 of geologists as to earthcjuake-fissures are untenable. He explained 

 clearly, aided by diagrams, the train of forces by which the elastic 

 wave of shock; on passing cut of the deep clay-beds where these 

 have a free side forming the steep river-banks, dislodges certain por- 

 tions and throws them off towards that free side — and that this is 

 but a case of the general b.w in accordance with which such elastic 



