786 GENERAL GEOLOGY OF MARULAN AND TALLONG, N.S.W., 



identified, however, north of Bungonia Creek. The possibility, 

 that the rocks in the Shoalhaven Gorge ma}^ be Devonian and 

 not Ordovician, must be recognised. 



Permo-Carhoniferous. 



Between the sediments so far mentioned and those which 

 succeed them, is a very strong stratigraphical break, indicating 

 the lapse of a vast interval of time. Permo-Carboniferous rocks 

 rest, with very strong unconformity, on the upturned edges of 

 Ordovician and Silurian (and possibly Devonian) sediments, and 

 on the eroded surface of the Glenrock grano-diorite. Our 

 district is almost the extreme south-westerly limit of Permo- 

 Oarboniferous rocks, and, naturally, the formation is compara- 

 tively thin and somewhat abnormal in character. 



Its base shows an extremely irregular line of junction with 

 the older rocks, indicating that the newer sediments were 

 deposited upon an eroded surface of considerable relief. Near 

 Bungonia Caves, the Lime-kilns, and on the Razorback there 

 occur small patches of Permo-Carboniferous rocks not more than 

 a few inches in thickness, the last remnants of a formerly con- 

 tinuous sheet. Northwards and eastwards the formation thickens 

 rapidly, until, at Badgery's Crossing, its representatives form 

 imposing cliffs, over four hundred feet in height. 



Of the horizons of the Permo-Carboniferous systems in the 

 type-district (Newcastle-Mai tland), two are represented at 

 Tallong, namely, Upper Marine Beds and Upper Coal Measures. 

 It is not always possible to distinguish between these, as both 

 alike are composed chiefly of very coarse conglomerates. Locally 

 the conglomerates pass into sandstones which are fossiliferous. 

 Elsewhere lenticular shale-masses are intercalated in the con- 

 glomerates. The conglomerates are very variable in thickness; 

 natural sections (Coal Mine Hill, Badgery's Crossing, etc.) expose 

 thicknesses up to 400 feet. 



Immediately in contact with the older rocks the conglomorate 

 passes into a breccia (Badgery's Crossing), composed of fragments 

 of the basement. At the locality mentioned, this has a thickness 



