HISTORY OF GEOLOGY AND PALEONTOLOGY. 



petrography, the geologists of Great Britain were not to the 

 front in continuing and advancing the new line of research. 

 It was not until Zirkel and Rosenbusch in Germany, and Fouque, 

 Michel-Levy, and Lacroix in France, had elaborated the new 

 system of research, and spread its teaching in the universities 

 by their text-books, that Great Britain took a more animated 

 part in the pursuit of petrography. 



In 1888, Mr. Frank Rutley published a book on Rock-forming 

 Minerals, in which he described the optical and chemical 

 properties displayed by the different minerals on microscopic 

 investigation. In the same year a book on British Petrography 

 was published by Mr. J. J. Harris Teall. The chief purpose of 

 the handbook was to bring the newest methods and results 

 of petrological research within the reach of a large circle of 

 British students and geologists. The work deals with the 

 eruptive rocks that occur in Great Britain; it begins with a 

 lucid discussion of ground-mass and the rock elements that can- 

 not be mineralogically identified. Frequent reference is made 

 to the investigations of Sorby and Vogelsang. The chemical 

 composition of the eruptive rocks is fully treated, having 

 respect to the researches of Bunsen. In discussing rock- 

 texture, Mr. Teall attributes great importance to the size and 

 development of the individual mineral components. The 

 features enumerated as valuable for the systematic arrange- 

 ment of the rocks are (i) the chemical composition, (2) the 

 mineralogical composition, (3) the texture, (4) the occurrence, 

 (5) the origin, (6) the geological age, (7) the locality. As, 

 however, the chemical composition cannot be judged from a 

 hand-specimen, Mr. Teall applies the mineralogical composition 

 as the primary means of classification, and uses texture for the 

 differentiation of sub-groups. The work concludes with very 

 valuable remarks on the origin and the metamorphoses of the 

 crystalline massive rocks. 



During the same year Rosenbusch published a second edi- 

 tion of his Mikroskopische Physiographic der massigen Gesteine, 

 In this edition he entirely withdrew his former principle of 

 classifying the rocks primarily on the basis of their mineralogi- 

 cal composition. Laying down as a fundamental principle 

 that a natural classification of the rocks ought to reflect the 

 genetic relations, Rosenbusch contended that rock-structure 

 offered the most reliable basis for the construction of a natural 

 system of the massive rocks. He pointed out that the struc- 



