334 ME. T. STEPHENS ON INTRUSIVE DIABASE [May I9OO, 



taken in Tasmania. All that can be done at present is to collect 

 materials for safe generalization by noting and sifting the. evidence 

 obtainable from natural sections, or otherwise ; and the primary 

 object of this paper is to correct a misapprehension which appears 

 to have been founded upon a paper brought before the Geological 

 Society rather more than half a century ago. 



In the Quarterly Journal for 1847 appears a communication by 

 the late J. B. Jukes 1 w 7 hich gives an admirable general description 

 of the chief geological features of the south-eastern portion of 

 Tasmania. Speaking of these in general terms, and remarking that 

 he had no time for a detailed examination of the country, the author 

 says (op. cit. p. 245) : — 4 The two principal rock-masses of the south- 

 eastern portion of Tasmania are a very massive, rudely columnar 

 greenstone, and the sandstone of the Palaeozoic formation .... The 

 sedimentary and the igneous rocks are so interlaced and entangled 

 one with the other, and their apparent relations at the surface so 

 different in different localities, that nothing, but a careful and 

 minute survey, laid down on maps of a large 1 scale, will ever be 

 able thoroughly to elucidate them.' Of the relations of the 

 sedimentary rocks to the greenstone of Mount Wellington, Jukes 

 speaks in carefully guarded terms ; but he mentions two sections 

 on the other side of the Derwent estuary, as affording evidence of 

 the non-intrusive character of the igneous rock. With reference 

 to one of these, which is described as being ' about a mile from a 

 place called Ralph's Bay Neck, on the S.E. side of North Bay,' he 

 says (op. cit. pp. 246-47) : — ' In this case a dark, rudely columnar 

 trap-rock ended in a succession of small cliffs and terraces in one 

 direction, upon which terraces and against which little cliffs rested 

 the sandstone perfectly undisturbed, and evidently in the position 

 in which it had been originally deposited. A parallel instance 

 was observed in the cliffs a little to the eastward of the entrance of 

 Port Arthur. It appears, then, that there are masses of greenstone 

 both of more ancient and more modern date than the Palaeozoic 

 rocks.' 



When my attention was first called to this passage, I had some 

 difficulty in determining the position of the section described, for 

 no such name as North Bay appears on any map of the present 

 day. Ralph's Bay Neck was easily identified ; but I had already 

 examined all the coast-sections in the neighbourhood, except a 

 small projecting point on the shore-line of Frederick Henry Bay, 

 which was at the time inaccessible, owing to a high tide. A second 

 visit to this point cleared up all doubt as to its identity with the 

 first of the two places mentioned. Here, on the face of a cliff 

 rising to a height of about 80 feet above high-water mark, are 

 the ' small cliffs and terraces of trap-rock,' which, to an observer 

 at a distance, would appear to be supporting a mass of sandstone, or 

 other similar rock, * undisturbed and ... in the position in which 

 had been originally deposited.' 



' Notes on tbe Palaeozoic Formations of New South Wales & Van Dieinen's 

 Land,' vol. iii, pp. 241-49. 



