122 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May 1 894,. 



the Shap granite, these Authors state they have since learnt that 

 basic lavas are very widely distributed over the Lake District, and 

 that the rocks on the north side of the intrusion must be placed in 

 this division. Such rocks might with propriety be termed basalts, 

 although, on account of the absence of olivine, some petrographers 

 would prefer to call them basic andesites. The Authors again refer 

 to the action of ' weathering ' in connexion with this group, where 

 some secondary products have remained as pseudomorphs of the 

 minerals which generated them, while others, more soluble, have 

 become disseminated through the mass of the rock, and especially 

 collected in small fissures and in the vesicles with which the lavas 

 abound. The basic lava of Low Fell contains 51 per cent, of silica 

 as against 60 per cent, in the ordinary andesite, but nearly 3 times 

 the amount of lime. Accordingly in the metamorphosed rock we 

 find green hornblende more common than mica in the mass as well 

 as in the contents of the vesicles. The ashes associated with the 

 basic lavas, however, contain brown mica far more abundantly than 

 hornblende, and the reason for this is seen in their low percentage 

 of lime. Another principal difference is noticed in the abundance of 

 epidote. Special attention is also devoted to the metamorphism of 

 the infilled vesicles, and some important deductions are drawn from 

 the phenomena observed. 



After touching on some other points, the Authors conclude by 

 stating their belief that thermo-metamorphism is not accompanied 

 in general by any change in the chemical composition of the rocks 

 affected. The exceptions are the partial loss of water and the 

 expulsion, under certain conditions, of carbonic acid. In some 

 districts it might be necessary to allow for the introduction of boric 

 and hydrofluoric acids, but that does not apply here. Innumerable 

 facts, they say, point to the conclusion that no transference of 

 material has taken place except between closely adjacent points, and 

 they are led to enquire what is the radius of the sphere of influence. 

 This must to a certain extent vary according to the nature of the 

 substance, and we must expect to find it greater at higher tempera- 

 tures. As a test-case, they take the production of lime-silicates at 

 the expense of calcite, and conclude that somewhere about -^ inch 

 would indicate the distance to which the interchange of lime and 

 silica has demonstrably taken place. The impression produced by 

 the study of other metamorphic minerals is in general accord with 

 the above conclusion. Moreover, the dependence of the range 

 of transfer of material upon temperature is well illustrated in the 





