THE MBTAMORPHIC ROCK8 OF ADBLIE LAND. 8TILLWELL. 43 



Both analyses bear marked resemblances to analyses of basic igneous rocks. While 

 this could be illustrated by comparison with numerous examples, it is well illustrated 

 by assuming the rocks to be igneous and then treating them in accordance with the 

 principles of the American Classification of Rocks. No. 153 is then a member of the 

 division Class II., Dosalane ; Order 4, Austrare ; Rang 3, Tonalase ; Sub-Rang 3, 

 Harzose. The examples of this division quoted by Washington* are chiefly afforded 

 by granodiorites, diorites, andesites, and porphyrites. No. 629 falls into Class III., 

 Salfemane ; Order 5, Gallare ; Rang 4, Auvergnase ; Sub-Rang 3, Auvergnose. The 

 examples quoted of this division include mainly diabases, gabbros, basalts, some 

 porphyrites, and camptonites. Both rocks, judged, therefore, from their chemical 

 composition, are likely to be metamorphosed basic igneous dykes. No. 153, being 

 more siliceous, probably approached rather towards a porphyrite, while No. 629 would 

 have probably tended to typical diabase or dolerite. The association with a meta- 

 morphosed granitic mass suggests their original character as basic lamprophyres ; but 

 the small percentage of the alkalies renders it unlikely. Metamorphosed lamprophyres 

 or lamproschiste are recorded from Garbh Allt, a mile S.E. of Glencaloie Lodgef, and 

 in the analysis the alkali percentage is as high as 6-95. The corresponding percentages 

 of these Cape Denison rocks are 4-71 and 2-79. 



It is now necessary to examine these analyses with the view of classifying the rocks 

 in Grubenmann's classification of the crystalline schists. Before doing so, however, 

 we give a resume of the method of classification as little or no use of it has hitherto 

 been made in the English language. In the present state of our knowledge of the 

 crystalline schists this classification has considerable value. It has been put forward 

 to organise our knowledge, but a more complete understanding of the metamorphic 

 processes and their products will cause, at least, modification. 



Grubenmann's Classification of the Crystalline Schists. 



Grubenmann has classified the crystalline schists primarily on a chemical basis. 

 The chemical data yield him 12 groups, each of which is divided into three sub-groups 

 which are based upon the typical features associated with the physico-chemical 

 conditions of his three zones of metamorphism. He has pointed out that classification 

 on any other basis, e.g., mineral composition, mode of origin, original character, etc., 

 will not succeed in bringing similar crystalline schists together, and, at the same time, 

 maintain their marked individuality which distinguishes them from the igneous and 

 sedimentary rocks. The variation, for example, of mineral content in this suite of rocks 

 under consideration, which bear strong chemical analogies, are similar in origin, and 

 have been subjected approximately to similar metamorphic conditions, is evident from 

 Table I. Mineral content is, therefore, useless as a classificatory basis if the classification 



" Chemical Analyses of Igneous Rocks," H. 8. Washington. Professional Paper, No. 14, U.S. Geol. Sunr., 1903. 



t " The Geology of Ben \Vyvi, Cam Chuinneag. Inchbae, and the surrounding Country." Memoir Geol. Surv. Scot., 

 No. 93, 1912, p. 125. 



