^ Analyses of Books. [Jan. 



Hare instances of permanent eruption (as at Stromboli) are 

 attributed to peculiar circumstances in the external figure and 

 position of the volcano, owing to which the erupted matters 

 escape from the orifice exactly in the ratio of the intumescence 

 that takes place below from the constant accession of caloric ; 

 the repressive forces being in this case preserved in equilibrio 

 with those of expansion. Such a volcano is of course as sensi- 

 ble as the barometer to all changes in the pressure of the atmo- 

 sphere, and this in fact appears to be the case with the pha^no- 

 mena of Stromboli. 



The author examines in detail, and by the strict rules of 

 physical science, the laws which must regulate all the variations 

 of the eruptive force, the duration of the quiescent intervals of 

 an habitual vent, the quantity of gaseous liquid and solid mat- 

 ters produced, the modes in which they dispose themselves, the 

 cooling and consolidation of lavas, their internal configuration, 

 texture, and mineral characters, their subsequent alteration by 

 acid vapours, or other agents, &c. and accompanies this inves- 

 tigation with corresponding facts from his own observation on 

 the recorded testimony of others. Many of these are new, and 

 highly interesting. Thus the great bulk of Trachytic when 

 compared with basaltic lavas, is proved to be owing to their 

 inferior specific gravity; examples are adduced of trachyte. 

 alternating in beds or currents with basalt ; volcanic mountains 

 are shown to be subjected to a process by which their great 

 craters are alternately hollowed out by paroxysmal eruptions, 

 and by degrees filled again to overflowing by the products of 

 less violent explosions; the origin of trass, moya, and some 

 tufas, is found in the bursting of lakes formed within the craters 

 of trachytic volcanos ; and it is shown that eruptions may be 

 continually taking place from numerous vents at the bottom of 

 the ocean without occasioning any visible commotion on its 

 surface, until the summit of the submarine volcanic mountain is 

 raised to within a short distance of that level, &c. 



Every volcano is thus either a permanent or intermittent issue, 

 by which the caloric of the interior of the globe passes off' into 

 outward space. By the more or less complete obstruction of 

 these vents, it is forced to accumulate on different points beneath 

 the superficial strata of the globe, until, by dilating the rocks in 

 which It resides, it produces fractures sufficiently deep and large 

 for its partial escape. In this manner the draught of caloric is 

 often forced to shift its direction, and is diverted from one vent 

 to another, the former becoming apparently extinct. In fact, it 

 is observed that an eruption is seldom repeated a second time 

 from precisely the same fissure ; and in the same manner as a 

 narrow cleft is sealed up by the consolidation of the vein of lava 

 it contains, or the accumulation of loose fragments above it, and 

 the local expansive force of the heated lava helo\v, checked for 



