Mammalian Remains from Grays Thurrock

H. Falconer
1863 The Geologist  
CORRESPONDENCE. 4 5 7 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 eicited my admiration. His views, to which he recalls my attention, 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
more » ... ed as a speculative idea, whether the crystallization of vast rocks could give rise, by their expansion or contraction, to the rupture of rockstrata 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 diminished volume of the crystalline mass, was sudden. The crystallization of rock-masses I be:ieve 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. I 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 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 volcanic 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 arid 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. -E D . GEOL.}
doi:10.1017/s1359465600000721 fatcat:2qwpq46mvvcipm4q3vj5ppdxzu