83 



of augite in well developed crystals." " These mineral 

 differences are however no criterion of age ; for we have here 

 genuine miocene basalts which can, mineralogically, not be 

 distinguished from recent pliocene ones. If the feldspar were 

 replaced by Nephelene or Leucite throughout a basalt sheet, we 

 might perhaps be justified to declare the geological age, within 

 certain limits, different from that of an adjoining feldspar 

 basalt flow, but even in this instance great care is required, 

 especially if conclusions are to be drawn as to the age of 

 underlying rocks." Happily we have now a more reliable 

 index to the age of the underlying rocks than may be ob- 

 tained from the comparative analysis of the constituents of 

 igneous rocks ; it is, however, satisfactory that the learned 

 professor's analysis tends to confirm the opinion which I 

 formerly entertained, viz., that the protecting cap overlying 

 the marine beds at Table Cape is a recent hasalt, and very 

 slightly differs from a similar flow which overspreads the 

 lignites at Breadalbane. 



In order to ascertain whether the intrusive rock, mentioned 

 by Mr. Allport in connection with the Travertin at Geilston 

 Bay, is of a similar character to the rocks at Breadalbane and 

 Table Cape, Professor Ulrich has, in a letter to me, kindly 

 volunteered to analyse any specimens from that quarter sent 

 to him. For this purpose, Mr. Allport, on being applied to, 

 at once procured and forwarded an interesting suite of speci- 

 mens. It will be of great value to have an established rela- 

 tionship with the various basaltic rocks in Tasmania and Vic- 

 toria. The rock known as the " older volcanic " in Victoria is 

 very similar to the rock at Table Cape, and, like it, the " older 

 volcanic" frequently caps the marine beds considered to 

 belong to the miocene age.* 



I regret that I could not find an accessible spot to ascertain 

 whether the sandstone, upper bed, was altered at point of 

 junction with the basalt or not. Perhaps some future ob- 

 server may be more fortunate in this respect. 



TUERITELLA GEOUP [h.) 



Following the descending order we come upon the group of 

 beds which immediately underlie the basalt as already 

 described. The group has been named by me in the diagram 

 as the " Turritella Group," because the small shell, T. 

 warhurtonii (Tenison- Woods), so abounds through this 

 particular formation as to give it a character which would be 

 sufficiently distinctive when compared with the only other 



* I have since been informed by Mr. Ulrich that the composition of the 

 intrusive rock at Geilston Bay is similar to that at Breadalbane and Table 

 Cape. 



