18 DE. THOMAS STERRY HUNT ON THE 



general theory of transmutation ; bj^ which it was imagined that a part or the whole of the 

 original elements of a rock might be replaced, thus giving rise to new lithological spe- 

 cies. Such a change has been appropriately named a metasomatosis or change of body. 

 I have elsewhere pointed out that this view has been adopted by two distinct and, to a 

 certain extent, opposed schools in geology, both of which, however, agree in admitting an 

 almost unlimited capacity of change of substance, through aqueoixs agencies, in previously 

 solidified rocks. The first of these schools applies the doctrine of metasomatosis to silicated 

 and aluminous rocks, either of plutonic or plutonic-detrital origin ; the second to rocks of 

 generally acknowledged aqueous origin, such as limestones.'' 



§ 36. As regards the metasomatosis of plutonic or plutonic-detrital rocks, such as the 

 ordinary feldspathic types, — granites, gneisses, diabases and diorites, — we are taught the 

 conversion of any one or all of these into serpentine or into limestone. The integral change 

 of each one of these into serpentine by the complete elimination of alumina, alkalies and 

 lime, and the replacement of these bases by magnesia and water has, as is well known, 

 been maintained by many writers of repute, including Miiller and Bischof, and later Dana 

 and Delesse. Moreover, King and Rowney have, since 18*74, taught the conversion into 

 limestones of all the silicated rocks mentioned, and have assigned a similar origin to the 

 great iuterstratified masses of crystalline limestone which are found in the ancient gneis- 

 ses, alike of North America and Europe. Not content with this, they have even maintained 

 the conversion of serpentine itself into limestone, and have explained the existence of 

 ophicalcites, and of serpentine masses in limestone, as evidences of the incomplete trans- 

 formation of beds of serpentine, itself the product of a previous transformation of 

 feldspathic rocks. ^ The older school of metasomatists regarded serpentine and other 

 hydrated magnesian silicates, on account of their insohibility, as the last term in the 

 metasomatic process ; but King and Rowney contend that serpentine itself is not exempt 

 from change. 



§ 3*7. Among the gneisses and mica-schists of the Atlantic belt are found at many 

 points, especially in Pennsylvania and thence southwestward through the Carolinas into 

 Alabama, important masses of a rock composed essentially of a chrysolite or olivine, and 

 referred to dunite or Iherzolite. "With these are associated not only serpentine but various 

 hornbleudic and feldspathic rocks, together with much corundum — the latter alike in 

 segregated veins and disseminated in the beds. These chrysolite-rocks, which, as seen in 

 North Carolina, were already described by the writer, in 18*79, as indigenous stratified 

 deposits in the Montalban series," have been made the siibject of detailed stiidies both by 

 Grenth and by Julien, whose published results are instructive examples of the application 

 of the metasomatic doctrine in the hands of its disciples. Genth supposes that, at the time 

 when these chrysolite-rocks were deposited, vast amounts of alumina were set free by 

 some unexplained process, and formed beds of corundum, and that this species, by sub- 



^' See, in this connection, Hunt, Cliem. and Geol. Esfsays, pp. 316, 320, 325 ; also preface to the second edition 

 of the same, pp. xxvii-xxsi.; and farther, Trans. Roy. Soc.,Can., vol. i., part 4, pp. 168-20-1. 



*'Chem. and Geol. Essays, p. 324; also Trans. Eoy. Soc. Can., I., part 4, p. 204; and W.King and T. H. 

 Rowney, An Old Chapter of tlie Geological Record, 1S81, chaps, vii. and xii. 



™ See James Macfarlane's Geological Handbook, 1879, p. 130 ; and, for some notes on the history of similar rocks, 

 Tran. Roy. Soc. Can., vol. i., part 4, p. 210. 



