BY H. 



JENSEN. 



563 



they all belong to one rather long period of volcanic activity, 

 probably, for reasons given later, lasting from the Eocene to the 

 Pliocene. In the preceding paragraphs the lavas are mentioned 

 practically in the order of sequence. South of Black Mountain 

 basalts cap trachydolerites and are unquestionably the last out- 

 pourings. North of the Warrumbungle Range around Bugaldi 

 basalts cap trachytic and phonolitic rocks. The age of the dark 

 green or blue trachj^tic rocks (with associated phonolites) relative 

 to the light grey arfvedsonite trachytes is harder to decide. At 

 Mount Caraghnan there is a capping of the former on the latter; 

 but more usually, excepting in the central mass of mountains, 

 the light grey trachytes exist only as isolated knobs, either stand- 

 ing in a valley surrounded only by sandstone and occasionally 



Fig. 3. — Diagrammatic Section from the Warrumbungle Eange to Jack 

 Hall's Creek through Timor Rock. 



tuflf as Wallaby Rock near Uargon Creek (see Figs.l and 5 posiea), 

 Scabby Rock (Figs. 4a and b), Timor Rock (Fig. 3); or surrounded 

 by tuffs, and sometimes capped with basalt as at Gowang; or 

 completely surrounded by the dark variety of trachyte, as Paddy's 

 Rock in the Naman Ledges. This last kind of occurrence 

 suggests that the more acid rock has been thrust into the more 

 basic, a sequence which is not verified by occurrences elsewhere. 

 The only explanation which satisfies all the facts is that the arfved- 



