18 REPORT—1850. 
remarkable work upon the subject, though very much overlooked. His 
principal views are best given in his own words. 
He commences by refuting the notion, that there is any necessary con- 
nection between the air, or the weather, or state of moon and tide and earth- 
quakes. 
And assuming then that they have an origin under ground, he enunciates 
the following propositions, sustaining each with its appropriate facts: — 
Ist. The same places are subject to returns of earthquakes, not only at 
small intervals for some time after any considerable one has hap- 
pened, but also at greater intervals for some ages. 
2nd, Those places that are in the neighbourhood of burning mountains 
are always subject to frequent earthquakes, and the eruptions of those 
mountains, when violent, are generally attended with them. 
3rd. The motion of the earth in earthquakes is partly tremulous and 
partly propagated by waves, which succeed one another, sometimes at 
larger and sometimes at smaller distances; and this latter motion is 
generally propagated much further than the former. 
Ath. It is observed in places which are subject to frequent earthquakes, 
that they generally come to one and the same place, from the same 
point of the compass. I may add also, that the velocity with which 
they proceed (as far as one can collect it from the accounts) is the 
same, but the velocity of earthquakes of different countries is very 
different. 
5th. A great earthquake (such as the Lisbon one) has been succeeded 
by several local ones since, the extent of which has been much less. 
From a discussion then of the known facts of volcanoes, he concludes, 
** That in all probability the fires of voleanoes produce earthquakes. That, 
however, the vibrations, &c. felt close to voleanic foci, either at their first 
formation or after, are not of the precise nature of earthquakes, or at least; 
differ in degree from them: and that— 
“ΤΠ greater earthquakes seem rather to be occasioned by other fires that 
lie deeper in the same tract of country, and the eruptions of voleanoes which 
happen at the same time with earthquakes, may with more probability be 
ascribed to those earthquakes, than the earthquakes to the eruptions, when- 
ever, at least, the earthquakes are of any considerable extent.” 
He then proceeds to give, considering the time he wrote, a wonderfully 
large and accurate view of the general conformation of the superficial crust 
of the earth, its arrangement into strata and beds, their relative position and 
co-ordination at distant places as to horizon, the nature of faults, dykes, &c., 
and from all he concludes that “from the want of correspondence in the 
fissures of the upper and lower strata, as well as on account of those strata 
which are little or not at all shattered, it will come to pass that the earth 
cannot easily be separated in a direction perpendicular to the horizon if we 
take any considerable portion of it together; but in the horizontal direction, 
as there is little or no adhesion between one stratum and another, it may be 
separated without difficulty.” 
After this he endeavours to show that the explosive power of volcanoes is 
due to pent-up vapour or steam, produced by the contact of water with 
masses of incandescent matter in the earth; that the alternate repose and 
activity of their action may be accounted for on this hypothesis, and that the 
expansive force is adequate to the phenomena, &c.; and having established 
this mechanism, he proceeds to announce the precise mode of formation and 
of propagation of the wave, in which he conceives earthquake motion to 
consist: he says, “ As a small quantity of vapour almost instantly generated 
