372 On Mineral Metamorphism. 



ble .and dolomite, and ends with the lavas of modern date. 

 or the trachytic rocks, granites and syenites are most closely 

 allied to the metamorphic slates ; the felspar porphyries form 

 a middle link between the granites and the prismatic tra- 

 chytes, which had formerly been in a state of fluidity. 

 Amongst the trap-rocks, the diallage-traps which occur in 

 rare instances only as eruptive veins, and never with a pris- 

 matic character, come nearest to the neptunian rocks ; after 

 these diallage-traps come the hornblende-traps, the metamoi'- 

 phosis of which takes place quite as frequently in a solid as 

 in a fluid condition : last of all come the augitic-traps, to which 

 class belongs basalt, almost identical with augitic lava. In 

 several important cases, it is difficult to determine to what 

 degree the metamorphosis has extended, since it remains un- 

 certain whether the form and structm*al relations of the 

 mountain-mass are to be considered as remains of the nep- 

 tunian sedimentary foi'mation, or as a product of the metamor- 

 phosis itself ; for the original form of the neptunian, as well as 

 of the volcanic sedimentary rocks have often become so 

 changed by erosion, and so much alike in both classes of 

 rocks, that this distinctive character is wholly lost ; the slaty 

 or tabular structure of lava-formed rocks becomes so entirely 

 like the strati ti cation of neptunian formations, that we are 

 frequently puzzledregarding the explanation of this character.* 



* One of the earliest writers on mineral metamorphism was the celebrated 

 Captain-General of the Saxon !Mines, Charpentier ; but the world is indebted to 

 a remarkable man — the author of the famous Theory of the Earth, Dr Hutton 

 of Edinburgh, for the first broad view of tliis subject in his work on the Theory 

 of tlie Earth. Sir James llall and Professors Playfair ami Hope supported and 

 extended this doctrine; Hall, by liis celebrated experiments ; Playfair, in his 

 eloquent and classical " Illustrations of the Huttonian Theory ;" and Dr Hope, 

 by his admirable lectures on the subject in the class of Chemistry in our Univei-- 

 sity. It may be said of Hojje that the most brilliant part of his academical lec- 

 tures was that on tlie Huttonian Tlieory. The celebrated Dr Boue, our excellent 

 friend and former pupil, first made known, in detail, to Continental Geologists, 

 the views of Hutton on this subject ; about the same time, Thomson of Naples 

 illustrated the metamorphism of rocks founded on his observations made in Italy; 

 and more lately Keilhau and Scherer of Christiania, Von Buch, Bischof of Bonn, 

 Studer of Bern, and Ilaidinger and Morlot of Vienna, have eminently contri- 

 buted to this department of the geology of rocks. Note hy the Editor, Edin. New 

 Phil. Jour. 



