RESEARCHES IN THERMAL METAMORPHISM. 303 



of water at high temperatures, and to regard the new- 

 formed minerals as recrystallised from such solution. He 

 has made a special study of the amorphous matter, without 

 action on polarised light, which occurs in many of the 

 metamorphosed slates, etc., examined by him, and often 

 plays an important part in such "spots" as do not consist 

 of definitely individualised crystals. He finds gradations 

 from the perfectly isotropic matter in question, through 

 indefinite cryptocrystalline aggregates, into finely divided 

 mica with other substances not certainly recognisable. The 

 isotropic substance he believes to represent the result of 

 relatively rapid cooling of the supposed solutions, while 

 definite crystallised minerals represent, at the other extreme, 

 the result of slow cooling. Further he conceives such 

 solutions formed in the inner and intensely hot zone of 

 metamorphism to be capable of permeating the outer and 

 cooler zones and depositing there the dissolved material. 

 In this particular his views are at variance with some of the 

 conclusions which seem to follow from the observations of 

 others. The conception of bodily solution and recrystallisa- 

 tion going on in a rock mass, which nevertheless retains 

 not only its form but many of its minor structural characters, 

 is one which confronts us with obvious difficulties, and we 

 must be content to await further enlightenment as to the 

 rationale of the complex processes involved in the minera- 

 logical transformations of rock masses. 



BIBLIOGRAPHY. 

 PART 11. 



(19) WEINSCHENK, ERNST. Ueber Serpentine aus den ostlicJien 



Central-Alpen und deren Contactbildungen. Habilitations- 

 schrift, Munich, 1891. 



(20) Harker, ALFRED. Carrock Fell : a Study in the Variation 



of Igneous Rock Masses. Part i., The Gabbro. Quart. 

 Jour. Geo/. Soc, vol. 1., pp. 311-336, 1894. 



(21) Callaway, Charles. On the Production of Secondary 



Minerals at Shear-zones in the Crystalline Rocks of the 

 Malvern Hills. Quart. Jour. Geo/. Soc., vol. xlv., pp. 475- 

 501, 1889. 



