CORRESPONDENCE. 



457 



and his indefatigable and acute observation of volcanic phenomena, over a period of 

 many years, entitle his opinions to the most marked respect, and his excellent works on 

 the subject have always excited my admiration. His views, to which he recalls my at- 

 tention, had escaped me at the time of writing my article in the November number ; but 

 I made no reference to any authors or any published views, because I simply wished 

 to put forward what I only regarded as a speculative idea, whether the crystallization of 

 vast rocks could give rise, by their expansion or contraction, to the rupture of rock- 

 strata not necessarily in immediate contiguity with the crystalline mass, but held in a 

 state of tension by the difference in volume produced by crystallization. Mr. Scrope has 

 misunderstood me altogether in supposing I meant a sudden crystallization : what I 

 meant was, that the " snap " of the rock-strata, held in tension by the increased or di- 

 minished volume of the crystalline mass, was sudden. The crystallization of rock-masses 

 I believe to be very slow, perhaps often occupying enormous periods of time to effect 

 over great masses. Still, however slow the alteration of volume takes place, a tensile 

 strain must be continuously accumulating until it exceeds the adhesive force of the strata, 

 and then a "snap" occurs. T also referred in my remarks only to such earthquakes as 

 occur without visible or evident association with active or eruptive volcanic phenomena ; 

 such, for example, as the late English earthquake, or those so constantly taking place 

 in the neighbourhood of Cornrie, in Scotland. It seems to me that there are two 

 classes of earthquakes, one connected with volcanic phenomena, as stated by Mr. Scrope, 

 the other, simply "snaps and jars," without any connection with volcanic phenomena at 

 all, and produced by the crystallization, the drying and contracting, or increase of volume 

 by heat or other suchlike natural causes which are not dependent on subterranean vol- 

 canic materials, such as molten lava or the supposed incandescent internal fluid core of 

 our earth. ■ I put forth the idea of crystallization as one of the possible causes of what I 

 supposed to be non-volcanic earthquakes, with some timidity, knowing and appreciating 

 the labours of Mr. Scrope and Mr. Mallet, and the more so that I had had little time to 

 devote to the due consideration even of my own idea. I thought it one, however, worth 

 promulgating, and I am gratified to read the terms in which Mr. Scrope speaks of it. 

 — Ed. Geol.] 



Mammalian Remains from Grays Thurrock. 



Sir, — With a view to the settlement of some undecided points connected 

 with the "mammalian fauna" of the pre-glacial deposit, and of the post- 

 glacial high and low level gravels, etc., any geologists or palaeontologists 

 possessing collections from Grays Thurrock, or any of the other fossili- 

 ferous localities in the valley of the Thames, or corresponding river-valleys 

 in the south-east of England, will greatly oblige the undersigned, by com- 

 municating to him whether they possess good specimens, containing teeth, 

 of bears, or of hysenas ; and if so, what amount of evidence the specimens 

 present. 



H. Falconer. 



21, Park Crescent, Portland Place, Nov. 12, 1863. 



Mammoth Remains at Leicester. 



Dear Sir, — As it is of importance in these " drift-searching " days that 

 all remains found of mammals in the drift should be made known to your 

 readers, I have much pleasure in communicating to you that information 

 was this morning brought me of a horn or tusk, of very large dimensions, 

 had been laid open in a cutting for drainage in the valley of the Soar, in 

 the outskirts of Leicester, and near the village of Belgrave. 1 at once 

 proceeded to the President of our Philosophical Society, and obtained his 

 permission to secure it for our town museum ; and also to inform one of 

 our leading geologists, James Plant, Esq., of the fact. We drove to the 



VOL. VI. 3 N 



