GEOLOGY OF ERUPTIVE AND ASSOCIATED ROCKS, POKOLBIN. 391 



brownish colour, similar to that in other parts of the 

 district, with small phenocrysts of felspar showing macro- 

 scopically. The melanocratic variety is much finer and 

 more even grained, and is of a bluish colour, having the 

 general appearance of a rather light-coloured basalt. The 

 leucocratic type has the wider distribution, and is the older 

 of the two types: on top of it the Carboniferous sedimentary 

 rocks, represented by sandstones and conglomerates, have 

 been deposited. On top of the conglomerate are further 

 flows of trachyte, both the leucocratic and melanocratic 

 varieties, accompanied by dykes and sills in the conglomer- 

 ate. More basic rocks succeed, the most extensive and 

 important being a coarse agglomerate associated with basic 

 looking tuffs, which are capped by trachy-andesite and 

 andesite. The blocks in the agglomerate are often rounded, 

 giving the appearance of a coarse conglomerate ; they 

 include rocks of a felsitic nature, with pebbles of a green 

 tuffaceous-looking rock, and the cementing material is of a 

 dark basic appearance, but of undetermined composition. 

 The whole of this series is well exhibited on the long ridge 

 along which run the old and new roads to Matthews' Gap. 



Probably connected with the same outbursts is the inter- 

 mediate glassy rock or pitchstone, of which a couple of 

 isolated outcrops are found and of which an analysis is 

 given below, and the andesite in the N.W. portion of the 

 area. The most basic portions of the Matthews' Gap area 

 series are a flow of basalt and associated tuffs. 



The last phase of the volcanic activity of Carboniferous 

 age is represented by a flow of dacite, which partially con- 

 ceals the outcrop of many of the earlier rocks, and which 

 is immediately under the Permo-Carbonif erous conglomerate 

 in some places. Dykes of leucocratic trachyte in the 

 agglomerate and trachy-andesite may belong to the same 

 phase. 



