Memews — Richthqfen's Si/stem of Volcanic Bocks. 513 



(three-fourths of the whole), and that the same unfortunate mis- 

 conception has gone far to destroy the benefit that might have 

 accrued to science from the researches of an entire generation of 

 both German and French Geologists in -volcanic regions, had not 

 their interpretation of the facts before their eyes been blinded by 

 the influence of so great a name. I cannot hesitate to expi'ess the 

 opinion that until these vague and contradictory views of the 

 character of volcanic action are universally renounced, no progress 

 can be made towards a sound theory of the mode of production of 

 the class of Hypogene formations, from Obsidian and Pumice to 

 Granite itself. 



That the vast accumulations of Trachytic porphyry, and also of 

 basalt, which accompany and envelop the now or recently active 

 volcanic cones of Western America (as of Hungary and many other 

 localities) have sometimes issued from prolonged fissures, or from 

 so many points upon such fissures, as to combine to form vast 

 elongated ' masses,' while on other points where the eruptive 

 action has been more concentrated, or lasted longer, the lava has 

 accumulated over the vent in domes or cones, sometimes of enormous 

 magnitude, is in entire accordance with the normal action of volcanic 

 energy. Why then are the volcanic rocks that have assumed these 

 "massive" forms not to be called "the product of volcanos?" 

 Such a distinction cannot rest (as some might imagine) on the 

 absence among them of fragmentary ejecta, thrown up by ex- 

 plosive outbursts of vapour from a volcanic vent, for M. Eichthofen 

 himself, no less than Humboldt, declares that in America the amoimt 

 of pumice, ash, tuffs, and bi'eccias, that form part of his "massiva 

 eruptions," probably equals that of the more solid rocks. The 

 emission of these " massive eruptions " must then have been 

 accompanied generally by explosive aeriform discharges from some 

 neighbouring vent or vents. Where then, again I ask, is the dis- 

 tinction of such phenomena from those of "A'olcanos proper?" This 

 is not a mere dispute about words. The school in question maintains 

 that the vast accumulations of trachyte greystone and basalt met 

 with in countries admittedly volcanic, were "not produced by 

 volcanos," but in some non-descript manner; and that "volcanos 

 proper " are merely portions of these previously existing rocks 

 which, at some comparatively recent period, have been upheaved 

 bladder-fashion, and in some cases pierced with a hole which has 

 allowed the escape of vapour from beneath, throwing up and sprink- 

 ling around ashes and some minor dribblings of lava. Such a theory 

 of volcanic action I maintain to be demonstrably false ; and that, 

 on the contrary, all volcanic formations were produced by volcanic 

 action such as we see it in the present day, fracturing the surface of 

 the earth by earthquake shocks ; extruding through the fissures so 

 formed, on one or more points of them, lavas more or less liquid, 

 which accumulate round the vent ; expelling, in explosive jets of 

 vapour, fragmentary lava or broken pieces of the rocks through 

 which they have forced their way, and sometimes blowing up into 

 the air, by a series of such explosions, the whole mountain which 



VOL. VI. — NO. LXV. 33 



