BY G. D. OSBORNE. 167 



sive flows), the succession from hornblende-andesite through hypersthene-andesitic 

 pitchstone to a series of keratophyres, toseanites, and sodi-potassie rhyolites, with 

 associated fragmental rocks, has now been shown to be a recognisable and dis- 

 tinct assemblag'e all through the Southern Carboniferous areas. 



The Paterson flow, a toscanite in most places, although somewhat similar 

 under the microscope to the toseanites of the Volcanic Stage, is not grouped 

 with this stage since, as it may be extrusive, its inclusion would involve also the 

 inclusion of some 2000 feet of strata occupying the interval represented by the 

 Mt. Johnstone Beds of the Paterson Valley: a, procedure that would not be 

 satisfactory for reasons made apparent below. 



(iii.) Glacial Stage. 



The strata from the top of the Volcanic Stage to the base of the so-called 

 Permo-Carboniferous System. 



The grouping of the 2000 feet of tuffs, arkoses and conglomerates with the 

 Paterson toscanite and the Main Glacial Beds is necessary on account of the 

 discovery of a horizon of varves near Glenoak, a village four miles N.N.W. of 

 Seaham. These varves occur in the equivalents of the so-called Mt. Johnstone 

 Beds, some 1800 feet below what was previously considered to be the base of 

 the glacial beds at Seaham. It seems desirable to group together all the strata 

 containing definite evidence of glacial origin, or of deposition during glacial 

 conditions, even though they embrace a lava flow and tuffs; also, it must be 

 remembered that, sandwiched in among the varves and tillites at Seaham and 

 elsewhere, there occur tuffs and tuffaceous sandstones. Further support is given 

 to the establishment of the "Glacial Stage," in the occun-enoe, at its base, over 

 jtnost of the region investigated, of a coarse conglomerate — particularly so near 

 "Oakendale" — with a maximum thickness of 100 feet, which indicates that, fol- 

 lowing the eruptions of lava of the Volcanic Stage, a decided uplift occurred, 

 rejuvenating the streams which brought down coarse gravels and deposited them 

 on the surface of the last felsite,. the outpouring of which closed the epoch re- 

 presented by the Volcanic Stage. 



It is difficult to arrive at a ^scheme of classification suitable for all require- 

 ments. The method of employing local names has certain merits, but the scheme 

 used by Mr. Sussmilch was not sufficiently general ■ for the whole area, especially 

 in view of the fact that there is a greater development of the Volcanic Stage at 

 Mt. Gilmfn-e than at Martin's Creek. Also the separation of the Mt. Johnstone 

 Beds from the Main Glacial Beds is not now advisable on account of the oc- 

 cuiTence in both of glacially-produced rocks. 



Observations upon Kuttung rocks in other parts of the Southern Carboni- 

 ferous areas show the existence of the three well-defined stages. Thus in the 

 neighbourhood of Gosforth and Lamb's Valley, north-west of Maitland, W. R. 

 Browne has found the sequence to be basal conglomerates, followed by a series 

 of volcanic rocks of the • same general f acies as the Volcanic Stage, succeeded by 

 conglomerates, varves, a flow of toscanite and more glacial beds. 



Our knowledge of the Kuttung Series generally, and of its time-relations 

 to associated series in particular, is still incomplete and for this reason no terms 

 have been used in the classification which indicate geological time. Attention 

 may be drawn to the fact, that although the base of the Kuttung Series is well 

 defined in a broad sense, the upper limit is by no means so clearly fixed, and 

 from the results of research by Professor David in this connection, it is very 

 probable that in the future some of the strata now referred to the Permo- 

 Carboniferous System will have to be regarded definitely as Carboniferous in 

 age. 



