COAIi MEASURES OF N.S.W. AND ASSOCIATED ERUPTIVE ROCKS. 259 



doubtful, as Mi*. C. S. Wilkinson has pointed out, how far these 

 rocks owe their origin to the detritus from massive eruptives, and 

 how far they are formed of true tuffaceous material. The remark- 

 able freshness however and freedom from decomposition of the 

 fragments of felspar inclines me to the belief that their origin was 

 chiefly tuffaceous. If this latter surmise be correct the immense 

 development of tuffs in this formation may greatly account for the 

 rather sudden disappearance of Lepidodendron in the upper strata 

 of this group. 



(ii.) Subsequent. The eruptive rocks which have intruded into 

 these strata subsequent to the time of their deposition are chiefly 

 granitic quartz and felspar porphy rites, and dolerites, principally 

 the former, which are of earlier origin than the dolerites. 



Group II. 



(A.) Sedimentary. 



The formations belonging to this group, geologically considered, 

 form in New South Wales a single main coal-field, with a few less 

 important outlying coal-fields. The main coal-field commences 

 near Ulladulla on the coast, and extends northerly to Port 

 Stephens, then bends inland and tends via Maitland, Singleton, 

 Rix's Creek and Ravensworth to Murrurundi, thence to Gunnedah, 

 thence near Inverell and via Warialda to Yetman on the Queens- 

 land border. Its further northerly extension is masked by a 

 covering of such newer formations as the Rolling Downs Series, 

 and the strata belonging to this basin do not reappear at the 

 surface until the head of the Dawson River is reached. From 

 here they extend to a short distance beyond Fort Cooper, to the 

 north of which they have been isolated by denudation from the 

 outlying coal-field of the Bowen River. Still further north beyond 

 the Bowen River Coal-field Mr. R. L. Jack, p.g.s., the Government 

 Geologist of Queensland, has discovered a small outlying field near 

 Townsville, the strata of which contain Glossopteris, so that it 

 may be co-related with some of the formations in this group. The 

 Little River Coal-field between Cooktown and the Palmer Gold- 

 field is the northermost coal-field, so far as at present known, 

 belonging to this group, and may perhaps at one time have formed 

 part of the main basin. It owes its preservation, as Mr. Jack 

 has shown, to the existence of some very heavy trough faults, 

 which have dropped the whole basin deep down into the surround- 

 ing Devonian rocks. 



The main basin extends westwards in New South Wales from 

 the coast at Ulladulla towards the head of the Clyde River thence 

 in a north-westerly direction to Bundanoon, thence byway of the 

 Burragorang Valley to Hartley, thence via Wallerawang to near 

 Mudgee, and is perhaps united by way of the head of Cooyal 

 Creek, and of the sources of the Talbragar River to the Spicer's 



