VOLCANIC ACTION IN EASTERN AUSTRALIA. 403 



of the tail sheath, have been louud in the Canadian Deep Lead, 

 near Giilgong, in di'ifts, probably on the same horizon as those 

 associated with the basalts at Gulgong, and therefore Pliocene. 

 (On the occurrence of the genus Meiolania in the Pliocene Deep 

 Lead at Canadian, near Gulgong, by R. Etheridge, jun., Pahcon- 

 tologist Recvirds Geological Survey of New South Wales, vol. i., 

 part iii., pp. 149-152.) 



In the volcanic geology of Tasmania, as far at I am aware, there 

 have not of late been any important discoveries which necessitate 

 alterations or additions to my previous paper. The fact, however, 

 might be recorded here that subsequent to the Hobart Meeting of 

 the Association I have further examined the so-called diabasic 

 greenstones in the neighborhood of Hobart, in Tasmania, and 

 find them to be gabbros, as suggested by Captain Hutton, the 

 principal constituent minerals being diallage and triclinic felspar 

 with magnetite. 



This confirms the conclusion (already in my opinion sufficiently 

 clear upon stratigraphical grounds) that, as maintained by Mr. 

 Thomas Stephens, M.A., the " greenstones " of Hobart are intrusive 

 masses, probably of the nature of laccolites, which are certainly of 

 newer age than either the Permo-Carboniferous rocks of Hobart. or 

 than the Mesozoic coal measures of Newtown, Jerusalem, Fingal, 

 &c. 



It remains to summarise briefly the evidence bearing on the 

 questions discussed in my former paper as to whether volcanic 

 action was, in Australia, directly related to heavy sedimentation. 



The newly-discovered quartz-felsites of Back Creek do not as 

 yet afford evidence of any value, the conditions relating to their 

 development not yet having been determined. The felsitic tuff 

 bed at the base of the Ipswich coal measures seems at first sight 

 an exception to the general rule that volcanic action has usually 

 followed close upon the heels of heavy sedimentation. The fact, 

 however, must be borne in mind that it is more than probable that 

 previous to the outbursts which produced the Brisbane tuff 

 Permo-Carboniferous rocks were deposited to a considerable thick- 

 ness along a shore line, perhaps somewhat east of the present 

 shore line. In the Bowen River coalfield these sediments attain 

 a thickness of several thousand feet, and in the Hunter River 

 District of New South Wales are upwards of 10,000ft. thick n 

 Stratigraphical evidence points strongly in this direction, so that 

 the Brisbane tuffs were probably erupted subsequent to con- 

 siderable sedimentation, though long before the downward move- 

 ment of the earth's crust in that locality had ceased. 



Probably upwards of 3,000ft. of Ipswich coal measures were 

 then formed, and after some outbursts of lava, such as those 

 represented at Ipswich, and possibly also those of Rosewood, the 

 lower division of the Ipswich coal measures was slightly upheaved, 

 and the Toowoomba basalts then flowed over an eroded and 



