COEEESPONDENCE. 
457 
and his indefatignble and acute obsen ation 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 lime 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 nse, 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 crysialUzation : 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 volnme takes place, a tensile 
strain must be continuously accumulating until it exceeds the adhesive force of the strata, 
and then a "snap" occurs. 1 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 Comrie, 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 coimection 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 ow n 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 Be mains 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 palseontologists 
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- 
municatiug to him whether they possess good specimens, containing teeth, 
of bears, or of hya?nas ; and if so, what amount of evidence the specimens 
present. 
H. Falconeb. 
21, Park Crescent, Portland Place, Nov. 12, 1863. 
Mammoth Bemains at Leicester. 
Deae Sib,— As it is of importance in these " drift-searching " days that 
all remains found of mammals in the drift shoiild 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 
i the outskirts of Leicester, and near the village of Belgrave. I at once 
I 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 
