1879.] 



On Ophites and related JRoek-?. 



215 



a description of its fibrous, arborescent, coccolitic, platj, and other 

 ailomorpns. 



With reference to (D) "The origin of certain mineral, structural, 

 and chemical characters of ophites, &c," the subject is treated of 

 under direrezit heaiis : — (1 1 Fibrous layers in peridote from ElfdaLen, 

 in "graphic granite" from Harris, in perthite from Siberia, and in 

 other instances. (2) The alternation of different minerals in lami- 

 nated ophicalcite and ophi-malacolite has its parallel in other and 

 totally different rocks. (3) The change of the fibres of chrysotile into 

 aciculse. separated by calcareous interpolations, is illustrated by figures 

 taken from decalcified and polarised specimens of this allomorph from 

 Canada ; also from a characteristic specimen of the same from the 

 type-locality. Reichenstein. (4) Branching configurations, such as 

 are assumed by serpentine, are common in hemithrenes from widely 

 different regions : the authors refer to examples, showing that they 

 are residual, resulting from the waste of crystalloids of nialacolite. 

 Beautiful examples occur in the calcaire saceharoide (a hemithrene) of 

 St. Philippe, near St. Marie-aux-Mines, in the Vosges, rivalling those 

 in Canadian ophite : and not only are the associated lobulated grains 

 of pyrosclerite covered with a fibrous layer, closely resembling chrvso- 

 tile in structure ; but its fibres are occasionally converted into acicuke, 

 separated by films of calcite. (5) The presence of calcite under the 

 latter condition, and in connexion with configurations of serpentine 

 and malacolite, as well as lobulated grains of these and other minerals, 

 the authors ascribe to chemical changes si m ilar to pseudomorphism 

 among minerals. (6) It is contended that no minerals are incapable 

 of resisting changes of the kind, even those regarded as the most 

 insoluble. The experiments of Bischof, the Professors W. B. and 

 R. E. Rogers and others, show that hypersthene, enstatite, serpen- 

 tine, and various mineral silicates, digested in water containing car- 

 bonic acid, are convertible into carbonates. (7) Cases are mentioned 

 of rocks, essentially composed of mineral silicates, which have thus 

 become changed; as diorite from Jersey, granite and a porphyritic 

 feldsite from near Gralway, which have had certain of their mineral 

 silicates replaced by serpentine and calcite. 



The latter cases bring on a chapter (E) " On rock-metamorphism 

 generally.'" The authors divide metamorphic rocks into two groups — 

 mineralised, and methylosed ; the former consisting of members which 

 have had their original sedimentary components mineralised into 

 gneiss, hornblende-schist. &c. ; and the latter of members, thus mine- 

 ralised, but which, through the intervention of chemical reactions, 

 have been converted into ophites, &c. : methylosis is to rocks the same 

 as pseudomorphism to minerals. After briefly referring to the theory 

 promulgated by Leibnitz in his ' : Protoga?a.' ? which anticipated many 

 points now o-enerally held as to the origin of the metamorphics, they 



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