468 



THE GEOLOGIST. 



the substance and surface of the disturbed country, with immense rapidity, from a focal 

 point at a considerable depth. The velocity of the waxe-iramit very great (above 

 thirteen miles in a minute), but that of the pari ides in wave-movement comparatively 

 very small. The earthquake- wave, and, when subteiTaneau sounds occur, the sound- 

 wave, in the same preological formations, travel with the same speed, the sound-waves 

 through the sea and the air somewhat slower. Why no permanent change of the level 

 of the ground can be occasioned by an earthquake. The original subterranean impulse 

 pci cussive, 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 high tension 

 (high pressure), the heat of which, either directly or mediately and virtually, becomes 

 mechanical 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, direction, and velocity of earthquake-movements, called Seismometers and Seis- 

 moscopes, some of them self-registering. Application of the electric telegraph to Seismo- 

 metry. Nomenclature of the " Elements" of Seismology. The first exact investigation 

 of the phenomena of a great earthquake made by Mr. Mallet, in the case of that of 

 Southern Italy in 1857. Principal 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 Royal Society, to Mr. 11. Mallet and Dr. J. W. Mallet, 

 and also to Professor Alexis Perrey, of Dijon, Mr. D. Milne, and other contemporary in- 

 quirers. 



Lectuke VI. {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 Avhich 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 refers 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 I'esults of a secondary and local generation of heat, arising from a circula- 

 tion of Chemical affinities 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 earth'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. Q,uantity 

 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 QUEKIES. 



TriE Kellet Skull.— With reference to the observations made by 

 Mr. C. C. Blake and Professor Busk on this subject, I enclose the follovr- 

 ing further information. Captain Barrie, R.N., writes to me, under date 



