ON THE FORMATION OF CRYSTALLINE ROCKS 243 



plored the immense volcanoes of the two Americas, and Leopold de 

 Buch, who so profoundly studied the structure of the Canary islands, 

 have, upon other considerations, still further evinced the power and 

 universality of volcanic action, and the varied forms under which it 

 manifests itself. 



§ 2. Eruptive rocks. 



Auvergne, which, like Scotland, presents in its geological constitu- 

 tion features that command attention immediately, has likewise fur- 

 nished the first well-attested examples of rocks which, without having 

 come from the crater of a volcano, have, be3'ond a doubt, had an 

 eruptive origin. Desmarets recognized the igneous formation of basalt 

 during an excursion that he made in that country in 1763, and pub- 

 lished it in 1768;* seventeen years, therefore, before the publication 

 of the first memoir of Hutton. It was then that the long discussion 

 took its rise between the neptunians and the plutonists, a discussion 

 which sometimes degenerated into a keen dispute, and which, it is 

 remarkable, was prolonged for more than half a century after the 

 eruptive origin of basalt had been ascertained in Auvergne, in Italy, by 

 this same Desmarets, and in the Hebrides by his successor, Faujas 

 Saint Fond. It is evident from a report made by Cuvier, in 1808, that 

 the arguments of the school of Werner still preserved their prestige 

 even in a country where facts supported by so much evidence plead 

 on the opposite side, and where such remarkable examples of the 

 intrusion of rocks had been recognized by Strange, Hutton, Hauss- 

 mann, and Leopold de Buch.t Without doubt the question would 

 have been more speedily settled if European communications and 

 relations had in those days presented the same facilities as in our 

 own. 



§ 3. Formation of metalliferous deposits. 



Since it has been recognized that metalliferous veins, as Descartes 

 had inferred, have been filled by exhalations coming from the depths 

 of the earth, their study has contributed to throw light on the subject 

 with which we are occupied; of this we shall see the proof further on. 



§ 4. Mechanical dislocations of the crust of the earth. 



The formation of mountain ranges presents in its history phases not 

 less singular than that of eruptive rocks. 



* M^moires de I'Academie, 1768. 



f " It was in conformity with tbe observations of Desmarets that a volcanic origin was for 

 a long time attributed to all the basalts, rocks very similar to certain lavas. It appears, 

 however, that the formations which resemble lavas do not all have the same origin. Such 

 are the rocks called ivacks, which cover great tracts in certain parts of Germany ; they 

 are there perfectly horizontal, have no elevation that could be regarded as a crater, and 

 rest upon very combustible coal, which they have not altered. They are nut therefore 

 Toleanic. Werner had perfectly proved these facts, and as a result of his observations a 

 multitude of formations lost the origin attributed to them The opinion of Hutton and 

 James Hall that they were melted in situ at the time of a general and violent heating 

 of the globe will hardly hold good." Edition in 8vo., pp. 171 and 172. Desmerets was a 

 witness to all this lon'g discussion and of the report which thus condemned his conclusions, 

 for he died in 1815. 



