176 Reviews — Prof. Weinsdtencli — The Grapldle Mines of Ceylon, 



rocks. The existence of still younger eruptive masses of granite haa 

 not yet been demonstrated, for tlie few rocks as yet described from 

 Ceylon as granite are rather varieties of the granulitic series. 



Professor Weinschenck compares the Saxon and Ceylon granulites,. 

 thinking with. Naumann that the former are truly eruptive rocks. 

 Had the Ceylon rocks been studied before those of Saxony this view 

 would have been more widely held. They differ from the Saxon 

 rocks chiefly in their non-schistose character and coarser grain. 

 Lehmann regarded the peculiarities of the Saxon granulites as the 

 result of dynamo-metamorphism. He regarded the microperthitic 

 intergrowths of two felspars as the result of such a process, but as 

 these are characteristic of quite unaltered rocks in Ceylon they ma}"- 

 also be original in the Saxon rocks. The absence of sericite in 

 the latter presents a difficulty to those who favour the dynamo- 

 metamorphic view. Lehmann supposed that its place was taken by 

 biotite, but this mineral is not infrequently an original constituent 

 in Ceylon rocks. Garnets are characteristic of typical granulites,. 

 and their presence is the result of chemical peculiarities in the 

 magma or peculiar physical conditions obtaining at the time of its 

 consolidation. The chemical composition of Ceylon and Saxon 

 granulites resembles those of truly igneous rocks. Perhaps in 

 Saxony we are dealing only with the outer margin of an eruptive 

 mass intruded into surrounding schistose rocks, while in Ceylon 

 the heart of the eruptive mass is exposed. In both cases there has 

 been extensive magmatic differentiation, and this may be considered 

 characteristic of granulites in general. 



It is only in immediate contact with the graphite veins that the 

 granulite matrix is chemically altered and finally impregnated with 

 graphite. Fragments of rocks included in the veins are also speciallj^ 

 affected. In the altered rocks the felspars are largely changed to 

 nontronite, a feature associated with the occurrence of graphite in 

 the Passau district also. The pyroxenes change to a fine scaly 

 material with aggregate polarization. Mica and garnet alter les& 

 readily. Impregnation with rutile and titanite is characteristic, as 

 in the .Bavario-Bohemian area. Beside the rock fragments, pieces 

 of various minerals occur in the veins — quartz, pyrite, orthoclase, 

 raicroperthite, apatite, biotite, augite — the formation of these being- 

 previous to that of the graphite, while calcite, and sometimes biotite, 

 seem to have been deposited contemporaneously. 



In the Passau district (Bavaria) the formation of nontronite and 

 impregnation with graphite affect the whole schistose complex, 

 while in Ceylon the graphite occurs in veins. This difference 

 depends chiefly on the harder and more massive character of the 

 Ceylon rocks. In Ceylon, Siberia, and Cumberland the graphite 

 occurs in veins; in Passau and Taconderoga (U.S.A.) in veins and 

 beds ; in Bohemia in beds : these differences depend on the varied 

 character of the matrix and not on different modes of origin of the 

 graphite. Emanations of carbon monoxide, with or without 

 cyanogen-bearing compounds, may have given rise to the graphite 

 veins ; while the introduction of iron oxide and manganese peroxide 



