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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



and Merian found in the Alps of Glarus the fiyseh passing into 

 rocks as crystalline as the mica-schist and gneiss of St. Gothard and 

 Chamouny ; and Sir B. Murchison has shown that large portions 

 of the fiyseh in the Grisons have been converted into a crystalline 

 rock, and that in many places in the Alps, secondary and even tertiary 

 limestones are changed into saccharoid marble undistinguishable from 

 that which has been called primary. 



But it is obvious that the metamorphism of materials so very 

 different in their nature cannot have been brought about except by 

 very different chemical operations, and that it could not have been 

 produced in all by the materials having been exposed to a deep-seated 

 internal heat ; for the altered rocks alternate with others of vast 

 thickness which have undergone no change, and through which the 

 heat could not have been transmitted. It is nevertheless very 

 doubtful whether the term is ever applied without some vague, in- 

 distinct belief that internal heat has been the great agent in the 

 change ; this certainly is not a very philosophical state of mind, and 

 shows how much it behoves us to be cautious in the use of a term 

 involving theory unsupported by experimental proof. To the fact of 

 the change of structure we cannot shut our eyes ; it is plain and 

 palpable ; and we must give it a name ; but the name should be free 

 from any unproved theoretical import. No true theory of the earth 

 can be arrived at until the theory of metamorphism, in its various 

 phases, has been established on sound chemical principles by synthetic 

 experiments. 



I have already referred to the memoir of M. Daubre'e on Meta- 

 morphism, published in 1858. In the same year there appeared the 

 ' Etudes sur la Metamorphisme ' of M. Delesse. He truly observes, 

 at the very outset of his work, that " metamorphism comprehends 

 phenomena which are extremely complex, and which are for the 

 most part involved in great obscurity." He considers that the subject 

 is divisible into two distinct forms, — the one being normal or general 

 metamorphism, the result of causes most frequently invisible, and 

 which have operated on a great scale ; the other abnormal, or rather 

 special, metamorphism, the result of accidental causes, the effects of 

 which are of limited extent. It is to this last form, which he also 

 designates " metamorphism of contact," that this publication is con- 

 fined. But there can be no doubt that normal or general metamor- 

 phism is by much the most important subject for our careful study : 

 that of contact is only a subordinate branch of the great question. 

 Besearches and experiments relative to it are doubtless of great value 

 as indications of the causes of the greater operation, and as likely to 

 lead to some well-founded theory of the many phenomena of general 

 metamorphism. But the processes, whatever they were, must have 

 been veiy different which caused the alterations produced, on many 

 occasions, when an eruptive and a stratified rock came in contact, 

 and that transformation which has extended over thousands of 

 square miles. In the former case the rock affected and that affect- 

 ing are before us, and the change was probably the work of a com- 

 paratively short time ; while in the latter case all is hidden, and the 



