468 
THE GEOLOGIST. 
the substance and surface of the disturbed country, Avith iminense rapidity, from a focal 
point at a considerable depth. The velocity of the tvave-transit very great (above 
thirteen miles in a minute), but that of the pari id es in wave-movement comparatively 
very small. The earthquake-wave, and, when subterranean sounds occur, the sound- 
wave, in the same geological formations, travel with the same speed, the sound-waves 
through the sea and the air somewhat slower, ^'hy no permanent change of the level 
of the ground can be occasioned by an earthquake. The original subterranean imj)ulse 
percussive, or of the nature of a blow, and probably caused by the sudden formation, ex- 
trication from hydroplastic matter, expansion, or condensation of steam of bigh tension 
(high pressure), the heat of which, either directly or mediately and virtually, becomes 
mecbanical force. That force may also be exerted through the instrumentality of the 
molten rock itself, and originate earthquakes by the violent fracture of strata or other 
solid masses of the crust. Means and instruments for observing and recording the oc- 
currence, dii'ection, and velocity of earthquake-movements, called Seismometers and Seis- 
moscopes, some of them self-registering. Application of the electric telegraph to Seisnio- 
rnetrij. Nomenclature of the " Elements" of Seismology. The first exact investigation 
of the phenomena of a great earthquake made by ^Ir. Mallet, in the case of that of 
Southern Italy in 1857. Priucipal results of that investigation. Obligations of science 
on this new subject, regarded as one of accurate inquiry, due to the British Association 
for its Advancement, and the Koyal Society, to Mr. R. Mallet and Dr. J. W. Mallet, 
and also to Professor Alexis Perrey, of Dijon, Mr. D. Milne, and other contemporary in- 
quirers. 
Lecture YI. {Jan. 7, 1863.) — Central or internal heat of the globe ; its mechanical and 
physical and its chemical effects. Its operation, both direct and by the correlative forces 
into which it is converted, in the production of Plutonic and that of Volcanic and Seismic 
phenomena respectively. Compatibility, convergence, and probable identification of the 
thermotic theories of those phenomena, founded on the old conception of a primitive 
internal heat, with the theory which refei's them to chemical action, originally proposed 
by Sir H. Davy, and advocated by Dr. Daubeny, Professor Bunsen, and other chemists 
and geologists of the present time ; as argued in previous Lectures on Igneous Geology. 
The latter theory, thus regarded, supplies the superficial cause of high temperature in 
the earth's crust, shown, by the recent experimental and mathematical investigations of 
]Mr. W. Hopkins, to be required, in order to account for the observed increase of tempe- 
rature in descending within the earth. Volcanos and earthquakes, accordingly, probably 
the immediate results of a secondary and local generation of heat, arising from a circula- 
tion of Chemical aftinities in the alternate Reduction and Oxidation of Combustible Bases, 
and taking place in cavities of the superficial solid crust, in which earthquake-waves ori- 
ginate, and of which volcanos are communications with the surface. Such chemical ac- 
tion excited by the transfer of the eai'th's central heat towards the surface, occasioned by 
the change of position of the matter constituting the superficial crust, effected by the 
action of the Sun upon the exterior of the Globe. Theoretical indication, formerly ad- 
duced, of another source of terrestrial temperature, originating in the Correlation of 
Forces, and which also would excite chemical action and give rise to the same series 
of effects and phenomena. Transition from plutonic to volcanic action. Quantity 
of matter ejected by volcanos on the surface of the globe probably equivalent to that 
in which the series of physical processes commenced by the solar action in the atmo- 
sphere and the waters terminates by depositing on the bed of the sea, in the form of 
sedimentary strata. 
NOTES AND QUERIES. 
The Kellet Skull. — Witli reference to the observations made by- 
Mr. C. C. Blake and Professor Busk on this subject, I enclose the follow- 
ing further information. Captain Barrie, R.N., writes to me, under date 
