Nuneaton, Warwickshire. 



157 



laboratory of the Buiy Technical School in consultation with 

 Mr. G. M. Norman, B.Sc, F.I.C., A.R.C.S., and the results 

 obtained, together with recorded analyses (cited by Hatch) of other 

 camptonites and of a well-known picrite, are set Qut below : — 



The selvage rock, when examined in thin section, presents the 

 ordinary features of an andesitic basalt and calls for no special 

 description. 



Very little absorption of the shale by the igneous rock has taken 

 place at the junction, and the absorption zone is probably not more 

 than i in. wide. In sections showing the igneous rock and the shale 

 in contact, the former near its junction with the latter is very dark, 

 almost black, and quite opaque, due probably to the presence of free 

 carbon derived from the shale, on the solution of a very limited 

 amount of its alumina. The frequent occurrence of a pencil-like vein 

 of calcite crystals marking the contact plane indicates that the latter 

 became a plane of discontinuity after the intrusion, and, therefore, 

 that the intrusion was accompanied by a negligible amount of 

 chemical reaction between the igneous mass and the shales. 



The earthy material forming the veins and strings which penetrate 

 the shales recalls the ' white trap ' (kaolinized basalt) described by 

 Geikie l as penetrating Lower Carboniferous shales in the Lowlands 

 of Scotland. 



6. The Alteration produced in the Shales. 



In the main the alteration is of the low grade and small extent 

 usual for similar intrusions ; but a microscopic investigation of 

 certain portions of these shales in thin section reveals the presence 



1 Q.J.G.S., 1892, Pres. Address, p. 136. 



