COERESPONDENCE. 
45H 
In another chapter Davilla records the following fossils from 
Canstadt, therefore probably from the same beds as his Ornitholite : 
molar teeth of Rhinoceros, " TJne canine, blanche, a petites herborisa- 
tions bleuf.tres, adherente a une portion de machoire pareillement 
herborisee;" another tooth, " iVrborisee . . . son interiear est calcine 
et adhere fortement a la langue ; " six other teeth, " Scavoir, deux 
arborisees, de Canstadt, I'une de Ehinoceros,* I'autre inconnue,t 
deux simplement fossiles, dont une de Cheval dans son alveole. Pius, 
une portion de machoire aussi fossile, trouvee a Canstadt," and 
fifteen other bones unnamed. These memoranda would lead one to 
refer the Canstadt Ornitholite to the Pleistocene ase 
o 
{To he continued.) 
COEEESPONDENCE. 
On the Causes of EarfhquaTces. 
Sir, — The occurrence of an earthquake of unusual riolence in England 
has naturally given rise to very general inquiries and speculations on the 
nature and causes of these phenomena ; and various theories more or less 
ingenious, but, for the most part, vague and obscure, have been broached 
upon the subject in the different orcjans of public instruction. 
I have not, however, seen anywhere a notice of that simple, and to my 
mind conclusive, view of the question which I have put forward in my re- 
cent work on Volcanos, and I therefore venture to call your attention 
and that of your readers to it. 
I there refer (p. 294) " these sensible vibratory undulations of the earth's 
surface to the snap and jar occasioned by a sudden and violent rupture of 
solid rock-masses at a greater or less depth, and probably the instanta- 
neous injection into the fissures so formed of intumescent molten matter 
from beneath." I am hapjiy to find an almost complete accordance be- 
tween this view and that offered by yourself in your last number. But 
when you go on to su2fgest the sudden crystallization of vast underlying 
masses of mineral matter as the probable cause of such ruptures in the 
overlying rocks, I must part company with you. Why should we resort 
to imaginary hypotheses to explain that which, if nature is consistent with 
herself', is to be simply accounted for by well-known facts ? It is certain that 
the greater number of volcanic eruptions are preceded or accompanied by 
local earthquakes, evidently caused by tlie s})]itting and rending of the 
rocks that form the flanks of the volcano, or the surrounding area, by the 
expansion and rise of intumescent lava beneath. 
In these cases an actual escape of condensed vapour and molten mineral 
matter does generally take place. Not so, it is true, in the case of other 
earthquakes, which are usually (not always) felt over more extended areas, 
and therefore probably proceed from a focus of disturbance more deeply 
seated, so as not to admit of any outward discharge of erupted matter, 
gaseous or fluid, but which, nevertheless, are uudistinguishable from the 
former in their seismic phenomena, and therefore may well be believed to 
* Scheuchzer, Physiq. Sacree, pi. 48, fig. 18. f lb., fig. 18, altera. 
