MEMOIR OF LEOPOLD VOX BUCH. 367 



whicli he li.ad propounded, namely, that thci disorder of the primitive strata of 

 the globe pertains to a profound subterranean cause which is connected with 

 volcanic action ; that not only the basalts but all crystalline rocks have issued 

 from the earth in the state of lava, and that to the reactions of the earth arc 

 to be referred the elevation of mountains and that of entire countries,* such as 

 Sweden. 



In the winter of 1814, while absorbed in tliese thoughts, he found himself at 

 London, as he might at times be found everywhere, and there encoiuitered an 

 accomplished Norwegian, the botanist Smith. " Our conversation," says Von 

 Buch, " happened to turn on the facility witli which one may trans])ort himself 

 from that capital to almost every known region, and the desire of profiting by 

 it became so strong that we presently resolved to set out for the Canary 

 islands." A fortunate re:»olution, Avhich has endowed geology with a work 

 that will remain the mark of one of its most important advances. t 



The Canary islands had been already visi'ed by skilful observers, among 

 Avhom we may distinguish one of our former and most valued colleagues, M. 

 Cordier, the continuer of Dolomicu ; but hitherto they had only been studied 

 for themselves. Von Buch studied them in subordination and with reference. 

 to his general conceptions. 



His book is composed of two parts. The first embraces all the details of 

 description : the study of rocks, elevation of mountains, variations of climate, 

 &c. In the second and most important, the author sets forth, in a few pages, 

 equally admirable for precision of language and fullness of information, his 

 whole theory of volcanoes ; the result of long and critical observation of what 

 is most general and constant iu those grand but hitherto mysterious phe- 

 nomena. 



After succinctly defining a volcano to be " a permanent communication be- 

 tween the atmosphere and the interior of the globe," he distinguishes the effort 

 v/hich elevates from the effort which rwptures ; the first gives him what he calls 

 the crater of elevation, the second the crater of eruption. He shows that in 

 each volcano thei-e is a central point around which the eruptions take place, 

 aud that this central point is always the highcs»t summit — the j)eah — of tlu; 

 volcano. He. discerns, further, a common action between all the volcanoes of 

 the Canary islands, connecting with the peak of Tenerifte the eruptions of the 

 Isle of Palma, and these last with those of Lancerotte ; for these eruptions ar»i 



* It would be more exact to say the deration of entire countries and of mountains; for, a.f- 

 cording to Von Buch, it is the red porphyry which in the first instance elevates countries or 

 continents, aud the augitic, the black porphyry, which transpierces the red porphyry ai;d 

 elevates the mountains. 



"The upheaval of the pf/ro^-f/i if; porphyry is posterior to the fonnation of the red sand- 

 stone and of the calcareous strata; but these sandstones are essentially connected Avith the 

 formation of th(^ red porphyry, and can scarcely be separated from it. It follows that the 

 pyrogenic porphyry nmst have pierced the red porphyry as-well as the sandstone, and to have 

 pierced it, must have raised up this porphyry itseUV — Von Buch : Lctlre d M. dc Humboldt, 

 renfermant le tableau gcologiquc dii Tyrol meridional, 1822. 



'■ From these considerations, I should not liave been suqjriscd to see, somewhere in the ir- 

 terior of these valleys, pyrogenic porphyries below the red porphyry. I have, indeed, 

 fioupjht for them in the whole extent of this last formation, but almost everywhere without 

 success. I was more fortunate in descendino: the valley of the Avisio. After having been con- 

 stantly proceedinj^ on quartz-bearinp: porphyries as far as Cembra, at some leaij^ues above 

 the opening of that valley, I recognized below tluit place, and at the edf^e of a kind of plain, 

 a very considerable mass of the pyrogenic formation, Avhose black color contrasts singularly 

 with the red of the prevailing quartz-bearing porphyry, and wliich is decidedly distinct from 

 the latter. It is evidently a rock, whose mass pertains to the formuticin of tho pyrogenic 

 poiphyry. Its aspect clearly shows that it is engaged in tho red porphyry, <!xcept towards 

 the i)ase, where it is connected, probably, with a mass of the same nature, which extends uu- 

 di'.y all tho mountains of the Alps." — Ibid. 



t M. de Hiunboldt, in reference to this wo'k, said : " Leopold vouIJuch is the first who has 

 recognized the interconnexion and mutual de])eudonco of volcanic ;)h(.'Uomena, and Itiii 

 thciehj proved himself the greatest geologi-t of our epo"/'!." 



