Ch. XIV.l 



OF THE STRATIFIED ROCKS. 



309 



A TABLE 



OF THE COMPOSITION OF SOME ROCKS WHICH OCCUR IN THE 

 FOSSILIFEROUS GROUPS. 



It will also be remarked, in this and a succeeding table, 

 that porcelain jasper, and analcine, both of which are said to 

 have been formed by the metamorphic action of basalt on 

 sedimentary strata in Anglesea, contain an alkali. These 

 substances, therefore, differ from all similar altered rocks, 

 and must be added to dolomite in the list of exceptions. We 

 might attempt to solve this difficulty, by suggesting that, as 

 part of a bed of compact felspar often possesses a schistose 

 structure, as does also even a mass of crystalline lava, so 

 might this basalt, and the analcine might be confined to such 

 slate at the junction of the igneous and aqueous rocks ; or the 

 jaspideous rock might have resulted from the combination of 

 the fixed basalt with the shale at their point of contact. 



x 3 



