586 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



parts of the mountains, especially at the head of the Castlereagh, 

 Wandiallabah Creek and XJargon Creek.* 



(c) Coal and Ironstone. — I have seen specimens of good coal 

 from a well near Croxon's, a few miles south of Coonabarabran. 

 Whether it is of Permo-Carboniferous or Triassic age I do not 

 know, but this part of the country appears to me to be Triassic. 

 The Geological Survey Map has it Permo-Carboniferous. It is 

 quite possible that payable coal seams may be met with. 



It is of some economic interest too that there are throughout 

 the area many ironstone beds in the sandstones. Some of these 

 are so rich in iron that they will probably pay to work when the 

 railway system reaches the district and workable coal seams are 

 found. 



B. Petrology. 



Only volcanic rocks were of sufficient importance for the 

 purpose of my research to be given special mention in this part. 



In the present paper, as in my previous reports on the volcanic 

 rocks of East Moreton, I have purposel}^ avoided making 

 microscopic measurements, by the Rosiwal method, of the amounts 

 of different minerals in the rocks examined. Such determina- 

 tions have (according to my experience in the study of the rocks 

 of Prospect) great value when the rocks studied are coarse and 

 even-grained, and consist essentially of easily recognised minerals. 

 Then it is possible, by Rosiwal measurements alone, to obtain a 

 very good idea of the chemical composition of the rocks. How- 

 ever, recent researches especially have shown that even in these 

 ideal cases the method is inexact. 



The rocks discussed in this paper are une\ en- and fine-grained, 

 and porphyritic. Most have a very fine base. It is therefore 

 often impossible, without the very greatest expenditure of time 

 and patience, to decide the nature of each grain. The results 



* I have seen some very good fair-sized pieces of precious opal obtained at 

 the head of the Castlereagh River near Timor, and numerous small pieces, 

 the size of pinheads, obtained in vesicular trachyte in all parts of the 

 Warrumbungles, and especially from the localities mentioned above. 



