﻿xlviil PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I905, 



characters of the igneous rocks, and the geological history of the 

 volcanic regions which he visited. He was the first to introduce 

 modern petrographical methods into Prance ; and both by himself, 

 as well as in collaboration with M. Michel Levy, he improved and 

 extended those methods. Moreover, it is to the joint work of those 

 two investigators that we are indebted for the proof that many 

 igneous rocks and minerals can be produced artificially by pure 

 igneous fusion. 



One of the most important investigations carried out by Prof 

 Pouque is that which relates to the volatile products associated with 

 volcanic action. In these investigations he followed up the work 

 of his old master, Charles Ste. Claire Deville, who had already 

 pointed out that the dominant gases and vapours emitted from 

 fumaroles vary with the distance from the volcanic vent and with 

 the time which has elapsed since the period of maximum activity. 

 Pouque not only verified this law, but threw additional light 

 on the subject. He showed that the variations observed are not 

 due, as might be supposed, to the disappearance of certain gases 

 and their replacement by others; but that the hottest fumaroles 

 contain all the gases, and that the variations are caused by the 

 progressive disappearance of those which are least volatile as the 

 temperature falls. While carrying on these researches, which were 

 often attended with personal danger, he demonstrated the existence 

 of free hydrogen during the eruptions of Santorin, and thus proved 

 that real flames not only may, but actually do, exist in association 

 with certain types of volcanic activity ; a fact which had often been 

 denied. 



In connection with his elaborate investigations into the petro- 

 graphical characters of the lavas and other igneous rocks of 

 Santorin, he devised two new methods for isolating the different 

 mineralogical constituents, one depending on the use of the 

 electromagnet and the other on that of hydrofluoric acid. Both 

 these methods have proved to be of great general utility. 



But Pouque was not only an accomplished chemist, mineralogist, 

 and petrographer. He was also a geologist. The mutual relations 

 of the rocks in the field were carefully studied by him, and 

 the events of which they are the records were placed in true 

 chronological order. Thus, in his classic work ' Santorin & ses 

 Eruptions/ he shows that the earliest eruptions took place beneath 

 the Upper Pliocene sea, that elevation followed, that subaerial 

 activity resulted in the building-up of a central volcano, with 



