and the Nature of the Liquidity of Lavas. 129 
In the earlier volume of the two (the ‘ Considerations on Vol- 
canoes’), however, I certainly overstepped thiswholesome rule, by 
entering towards the conclusion of the work upon some rather 
crude speculations on a general theory of the globe; and this, 
together with defects of style and arrangement, and likewise of 
illustration, of which I became sensible only when it was too 
late to amend them, sufficiently accounts for the different re- 
ception these two works met with from geologists at the time. 
Neither, however, I presume to hope, were wholly without some 
beneficial result. At the period of their publication, the Wer- 
nerian theory of the precipitation from some aqueous menstruum, 
not merely of granite, and what were then called the primitive 
formations, but even of all the trap-rocks, still prevailed, and 
had the support of a large school of geologists in this country. 
I venture to think that the facts reported in my two volumes 
(especially those represented to the eye in the atlas illustrative 
of the volcanic remains of Central France) had some share in 
the final extinction of that German romance,—which some geo- 
logists as old as myself may remember to have been regarded 
almost in the light of a gospel-truth, and defended with all the 
acrimony of polemical controversy. 
Some of the opinions, however, expressed in these works with 
respect to the laws that govern volcanic action, were severely 
criticised at the time. Others have been since opposed by rival 
theories. And, as these disputed questions have an important 
bearing on some of the most interesting problems of geology, 
I trust it may not be unprofitable to call attention to the more 
prominent among them. 
I will advert on this occasion to two subjects especially, viz. 
I. The origin, or mode of formation, of voleanic cones and 
craters. 
II. The nature of the liquidity of lava at the time of its pro- 
trusion from a volcanic aperture. 
I. Formation of Cones and Craters.—In both of the works 
to which I have alluded, I referred the formation of those re- 
markable circular hollows, usually called craters, which are of 
such frequent occurrence in volcanic districts, to explosive aéri- 
form eruptions, breaking their way through the superficial rocks ; 
and that of the external more or less conical hill or mountain 
which generally, but not always, environs a crater,—and which, 
indeed, often occurs without a crater, but always characterized 
by the qui-qui-versal dip of its constituent beds of lava and 
conglomerates,—to the accumulation, round and above an erup- 
tive vent, of its fragmentary ejections and the lava-streams 
poured out from it. 
Phil. Mag. 8. 4. Vol. 14, No. 91. Aug. 1857. K 
