GEOLOGY OF ERUPTIVE AND ASSOCIATED ROCKS, POKOLBIN. 393 



the Upper Marine sandstones into juxtaposition with the 

 Carboniferous formations is probably part of the Elderslee 

 fault of Professor David which has caused the burying of 

 the Greta coal measures to a considerable depth. 



B. Permo-Carboniferous Rocks. . 



These have not been studied in detail, but their relation- 

 ships have been noted where they are contiguous with the 

 Carboniferous rocks. The most notable among the sedi- 

 mentary series is the quartz-porphyry conglomerate, which 

 in this district appears to form the lowest of the Permo- 

 Carboniferous strata. It has been suggested, however, 

 that any possible lower beds have been concealed through 

 overlapping. The conglomerate sometimes disappears and 

 then the eruptives are immediately overlain by the Lower 

 Marine sandstones. 



The igneous rocks are confined to basalt and tuffs con- 

 temporaneous in the Lower Marine. The position of these 

 is indicated in the geological map, and it will be observed 

 that in the southern portion of the district they exist as a 

 marginal belt to the Carboniferous rocks. They occur 

 some distance up in the Lower Marine, intrusive through 

 the basal conglomerate and some of the overlying sand- 

 stone. Their contemporaneity is proved by the presence 

 of Stenopora and Fenestella found by Professor David in 

 the associated tuffs on the western side of the Mount 

 Bright area. 



A considerable extent of the basalt on this western side 

 is amygdaloidal, the steam holes being filled with zeolites, 

 chiefly radiating aggregates of natrolite, often in fairly 

 large masses, with associated minor development of pinkish 

 datolite and analcite. It is a remarkable circumstance 

 that similar occurrences are not met with in the basalt on 

 the south and east of the area. 



