PEOCEEDIJTGS OF GEOLOGICAL SOCIETIES. 
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Lecturi; III. (Xov. 26.) — Volcanos mountains of ejection and accumulation, but uot 
of elevation. Researches on this subject of Mr. Scrope, Sir Charles Lyell, and M. H. de 
Saussure. Peculiar conical form and structure of volcanic mountains, their, dispositioa 
in groups or lines connected with fissures in the earth's superficial crust, and Geographi- 
cal Distribution. May be slowly or rapidly produced, but, when formed on the land, 
are always of long duration. Have probably existed at all known geological periods, and 
some which were active in the later Tertiary or Cainozoic eras are active now (as Etna), 
while others are extinct (as the volcanos of Central France and Asia Minor). One vol- 
canic cone may envelope and bury others in its ejections, or one chain of volcanic vents 
may overwhelm another under its lavas and tuffs, and so preserve them as a part of it- 
self, as observed in ^Madeira by Sir Charles Lyell and M. Hartung; but as volcanic 
cones cannot in any other sense become subterranean, nor long remain beneath the sea, 
there are not any Fossil Volcanos. Of those, therefore, which were active in the ^leso- 
zoic and Palaeozoic eras of geology, certain products only remain. Such products abun- 
dant in Britain, as exemplified in the middle series of Cambrian Slates, and the Western 
Islands of Scotland. In what manner volcanos are related to the elevation of the laud 
and of other mountains, and to the production of the actual surface of the globe. Pro- 
bably only the features of that surface produced by the direct action of the internal 
forces, as recently indicated by Mr. Jukes. Enormous mass of materials transferred by 
them from below to the surface. 
Lectuke IV. (Dec. 3.) — Volcanos not the cause of earthquakes nor earthquakes of 
volcanos, as commonly supposed ; but both the'"' manifestations of a common force under 
different conditions," or the partial effects of a common cause, or of a common series of 
causes, originating in the internal heat of the globe. Particular history of some of the 
most remarkable earthquakes. — Those of Lisbon, November 1st, 1755; Calabria and 
Sicily, February and March, 17S3 : Riobainba, iu Peru, February 4th, 1797, the greatest 
earthquake whose effects have been observed; Chile, February 20th, 1835, and concomi- 
tant volcanic phenomena; Southern Italy, December 16th, 1857. Succession of earth- 
quake phenomena when taking place on laud or under the ocean. The ground and all 
objects resting upon it suddenly moved backwards and forwards by an alternate horizon- 
tal motion, accompanied by a vertical or ujjward and downward motion. Duration of 
the shock. A continuous violent tremor often felt in addition. Great sea-wave attend- 
ing earthquakes. Sounds which accompany them when subterranean fractures occur. 
Earthquakes do not occasion permanent elevation or depression of the land or sea-bed 
(for reasons to be explained in the next lecture), contrary to what is often affirmed by 
geologists, though such changes of level may take place at the same time. Occur over 
all parts of the earth's surface, but certain areas of land and sea more subject to them 
than others. Geographical distribution of these areas, or Seismic regions, and its rela- 
tion to that of volcanos. In what manner the occurrence of earthquakes and the erup- 
tions of volcanos are related. Alleged and possible influence of the unequal attraction of 
the moon, and of the varying pressure of the atmosphere on the occurrence of earth- 
quakes. Certain districts of Great Britain subject to slight earthquake-shocks at the 
present time. 
Lecture V. {Bee. 10.) — The philosophy of earthquakes constitutes the new dcpart- 
meut of science termed Seismology. Analysis of their phenomena. The shock, or earth- 
quake-wave, a true roll, or continued undulation of the solid crust of the earth. Earth- 
quake-motion shown to be undulatory, or icave-like, by Michell, about a century ago; 
but erroneously assimilated by him to that of ordinary liquid superficial waves, such as 
those of the sea, which it only apparently resembles. The Dynaniics of Earthquakes first 
explained, and the true nature of their motion, as being that of a Wave of Elastic Com- 
pression, demonstrated, by Mr. Robert Mallet, in 1846. "Waves of elastic compression 
may be communicated to, or originate within, the substance of matter of every kind, 
aeriform, liquid, and solid ; as the atmosphere, the waters, and the earth ; becoming sen- 
sible as sound, in all three mediums, and also, in the case of the earth-wave, as Seismic 
or earthquake phenomena. These waves consist of an alternate condensation and rare- 
faction of the medium ; the particles of fluid or solid alternately approaching and receding 
from each other, in continuous succession, and in all directions from the central or 
focal point where the impulse takes place which gives origin to the wave. An earth- 
quake the transit or passage of such a wave, or of a succession of such waves, through 
