2 J. W. Jadd — On Volcanos. 



volcanic action on the earth and that of vital action in the human 

 body. In either case our opportunities for direct experiment are 

 comparatively few ; and in both, therefore, we are compelled to 

 resort to indirect means in order to attain the desired results. To 

 acquire an understanding of the nature and causes of vital action, 

 one class of inquirers — the Physiologists — study the phenomena 

 presented by the living body as it performs its various functions ; 

 while another class — the Anatomists — examine, in the dead subject, 

 the machinery by which the various processes are carried on, and the 

 structure which is built up by their operations. As in Biology, so 

 in Geology, we have inquirers investigating, by the aid of mathe- 

 matics, physics, and chemistry, the movements, products, and other 

 attendant phenomena of volcanic activity — the Physiology of the 

 Earth ; while others devote themselves to researches connected with 

 the position and relations of the masses which constitute it — the 

 Earth's Anatomy ; and these latter find in the ruins of extinct 

 volcanos, and the intrusive masses connected with them, alike the 

 mechanism and the products of igneous activity. There is, indeed, 

 this difference between the study of the Anatomy of the Microcosm 

 and that of the Macrocosm — that, while in the former we are able by 

 dissection to examine the structure of its parts at our will, in the 

 latter we can only attain our object by taking advantage of those 

 revelations of its interior, effected by the conjoint action of sub- 

 terranean movements and surface denudations. 



It will not, perhaps, be doing violence to our comparison, if we 

 venture to push it one step farther, and to remark that, as the pro- 

 gress of Biology has in recent years been very greatly furthered by 

 the microscopic study of the minute tissues of which organized bodies 

 are composed, so a new department of Geology has arisen — Micro- 

 petrology, the homologue of Histology — which promises equally to 

 advance our knowledge of the origin, nature, and succession of those 

 series of changes which constitute the "life of the globe." The 

 study of the internal structure of rocks by the aid of the microscope, 

 the initiative to which was given in 1858 by Mr. Sorby's remarkable 

 paper " On the Microscopical Structure of Crystals, indicating the 

 Origin of Minerals and Rocks," has recently, in the hands of Zirkel, 

 Forbes, Vogelsang, Rosenbusch, Allport, and a host of other enthu- 

 siastic observers, made most prodigious strides, and promises to 

 afford the most valuable aid to geological research. 



The first attempt at a general treatise on Vulcan ology was that cf 

 Mr. Scrope in 1825. Unfortunately, while following out the two 

 lines of inquiry which we have just indicated, and attaining many 

 important results, the correctness and value of which have been 

 established by subsequent investigations, the author permitted him- 

 self to be drawn aside from the true paths of geological inquiry into 

 the speculations of Cosmogony. No one was more conscious of this 

 blemish of his work than the author himself, as was shown by the 

 subsequent publication of his well-known work, " The Geology and 

 Extinct Volcanos of Central France," in which this error is most 

 carefully avoided; and also in a second edition of his general treatise, 



