32 NOTES ON THE GEOLOGY OF CRADLE MOUNTAIN DISTRICT, 



Mr. Montgomery records the presence of a thousand feet 

 of sediment beneath Barn Bluff. The basal beds at the 

 last locality comprise a hundred feet of conglomerate, fol- 

 lowed by two feet of cannel coal, enclosed in black micar 

 ceous shale containing GIoH^iopterh {omta /) and Xoeygera- 

 thiopsis sp. Above this lie nine hundred feet of marine 

 mudston©, shale, sandstone and conglomerate similar to 

 those occurring at Mt. Pelion, nine miles to the south- 

 east, which contain such typical Permo-carboniferous fos- 

 sils as FenesteHa, Spirifera, Productiis, AvicuJopecten and 

 Stenopora. (^) Mr. Waller has estimated the series at Mt. 

 Pelion to hQ> from a thousand to fifteen hundred feet 

 Ihick. C^) Thus the Permo-carboniferous basin becomes 

 deeper towards the south-east, and many of the outcrops 

 show a slight tilt in that direction. 



At the surface in contact with the overlying dolerite, 

 the mudstones are more or less altered, silicified and in- 

 durated. Small veinlets of opal traverse the bands of 

 black carbonaceous shale. The alteration does not extend 

 more than about a foot from the dolerite. It is well 

 exposed on the northern face of Barn Bluff. 



The Cretaceous dolerite caps Mt. Brown, Barn Bluff, 

 and Cradle Mountain. It has the same general characters 

 as the Mesozoic dolerite in other parts of the island, and 

 may be considered to be portions of sills once continuous 

 with the dolerites of the Pelion Range. Waller affirmed 

 this former continuity, but doubted the intrusive charac- 

 ter of the dolerite. (^) An examination of the base 

 of the dolerite on the northern face of Bam 

 Bluff, however, shows that it transgresses to a small 

 extent across the bedding planes of the miid 

 stones; and in the case of Cradle Mountain the doler- 

 ite rests on sandstones in the southern end, but on the 

 underlying basal conglomerate on the northern. No feed- 

 ing dykes were observed, but attention might well be 

 directed to the north-eastern foot of Cradle Mountain, 

 where, as seen from a distance, the dolerite appears to 

 pass down through the Permo-carboniferous rocks, to com© 

 into contact with the Pre-cambrian sch^!st. (See Plate 3.) 

 The dolerite on Barn Bluff is about 650ft. thick, that on 

 Cradle Mt. 700ft., but that on Mt. Brown is per- 

 haps not more than 300ft. Columnar structure is very 

 pronounced in the two former masses; but in places 

 the predominance of one direction of vertical jointing 

 cause® instead a platey structure. 



(6) See Bibliography No. 13. 



(7) See Bibliography No. 21. 

 t'8) Op. cit. supra. 



