9 



discussed most fully before the members of this Society,* and 

 which have subsequently received additional illustration in 

 the interesting j^aper by Dr. Barnard, in respect of the 

 vegetable drifts of Gulgong. In order that I may establish 

 the characters, relations, and position of this interesting for- 

 mation, which indeed lies within as well as around the fair 

 city of Hobart, I shall perhaps be enabled to do so more 

 effectually if, in the first place, I confine myself to a descrip- 

 tion of the principal sections as they occur at particular 

 places, some of which I have already referred to, viz : — One 

 Tree Point, Sandy Bay, Cornelian Bay, Pipe Clay Bluff, 

 Prince of Wales' Bay, Beauty Bay, Lindisfarne Bay, Geilston 

 Bay, and the neighbourhood of Burnet-street, Hobart. It 

 will be seen upon the Map which has been kindly prepared 

 for me by Mr. Frank Lovett that, on the one hand, all the 

 points lie within the basin, and are subject to the wasting 

 advance of the waters of the existing estuary ; while, on the 

 other hand, they abut against the older rocks, and the 

 eruptive diabase represented by Mount Nelson, Knocklofty, 

 the Domain, Mount Direction, the lofty ridge terminating in 

 Point Rosny, and the more distant but majestic crest of 

 Mount Wellington. 



These latter diabasic rocks constitute the chief characters, 

 and have rendered famous the features of our neighbourhood, 

 and they surround both city and the formation being 

 described, as with a great encircling arm. 



The formation at One Tree Point lies at the base of 

 Mount Nelson. It forms a gentle eminence of a triangular 

 shape, whose base, washed by the Derwent, stretches from 

 opposite Sandy Bay Point to a creek which runs into the 

 Derwent nearly opposite Trywork Point, while its apex lies 

 between two hollows which radiate from that elevated saddle 

 which forms so conspicuous a feature beyond the Flagstaff 

 Station, at Mount Nelson. 



A section underneath the new defence works on the Brown's 

 Eiver road presents the following appearance, which, with 

 some of the leaf figures, have been graphically sketched for me 

 on a larger scale by my friend Mr. F. Salier. (See Plate l.J 



The beds marked a. h. dip at a considerable angle to the 

 south-east in the direction of the existing channel. Were it 

 not that the laminae in the plane of bedding are rich in 

 certain well-known tertiary leaf impressions, the appearance 

 of some of the lower members of the group, A\4iich include a 

 motley assortment of coarse and huge angular blocks, princi- 

 pally of the fossiliferous mudstone of Palaeozoic age, would 

 be apt to mislead, and perhaps may have hitherto misled the 

 casual observer. 



* Proc. Roy. Soc, 1879. 



