330 Transactions. 



and the same beds cover a fair tract of country to the eastward, and finally 

 junction with the coal-measures which were described previously as occur- 

 ring in Broken River. This completes the reference to occurrences round 

 the whole circuit of the basin. 



In this account of the various localities where clear sections of the 

 lower members of the sequence of Tertiaries are given it will be noticed 

 that there is no indication of an erosion surface, and that the conformity 

 is complete. This has been admitted by both Hutton and McKay. This is 

 an important point, as will be further emphasized when the fossil content of 

 the tuff is considered. The presence of the volcanic-ash beds at different 

 horizons has been a matter of considerable difficulty, but in my opinion 

 the following is a fair statement of the conditions :- — 



1. Volcanic action commenced at the time when the white sandy beds 

 were being laid down— that is, between the deposition of the greensands 

 and the marl. 



2. Volcanic activity was more pronounced in the neighbourhood of 

 Coleridge Creek, the ash beds being there much thicker than elsewhere 

 in the area. The earliest signs of volcanic action are also furnished by 

 that locality. 



3. Elsewhere in the district the beds are thinner— in fact, they do not 

 appear at all in the sections in Waterfall Creek, where they should be easily 

 seen were they present. This remark applies to higher occurrences of the 

 ash interstratified in the limestone. 



4. This interstratification is not indicative of an unconformity, but 

 that the deposit of ash went on contemporaneously with the formation of 

 limestone and other marine beds in the adjacent sea. 



(b.) Occurrences of Limestone with Interstratified Tuff. 

 The limestones, which are in places separated by the uppeimost layer 

 of the volcanic-tuff beds, were considered by both McKay and Hutton as 

 quite distinct, and belonging to different geological periods. The present 

 author, however, regards them as belonging to the same period, with a 

 difference in character which any limestone might exhibit as the conditions 

 of deposit slightly changed during its deposition, the tuff bed interstratified 

 in the limestone having just the same geological importance as similar beds 

 interstratified in the sands and marls underneath the limestone. Before 

 considering this question in more detail it will be best to give some account 

 of the occurrences that the locality affords. 



The most typical section, and one which is free from disturbing elements, 

 is that obtained in the lower part of Home Creek, just above its junction 

 with the Porter River. The creek cuts across the strike directly, and 

 on the high walls of its gorge-like bed the relations can be easily seen. 

 (Plate XXII, fig. 1.) The following is a description of this section : — 



Limestone, 60 ft. thick, the upper 10 ft. or 12 ft. of white stone, the 

 lower 50 ft. yellowish and weathering greenish-grey where run 

 over by the stream ; the rock is almost entirely composed of 

 coralline fragments. 

 Calcareous volcanic tuff: This grades down from the overlying bed, 

 and the proportion of volcanic matter increases in the lower 

 part ; the approximate thickness is 10 ft. 

 Volcanic tuff, the upper part consisting of volcanic matter occasion- 

 ally weathering green, and passing down into volcanic tuff 

 weathering dark green, and finally into volcanic ash. the total 

 thickness being about 75 ft. 



