of the Island of Tasmania. 161 



to the rest we may pay that there is an extreme proba- 

 bility that it has not. It is true that we have evidence of 

 immense denudation in the greenstone, and that in north- 

 east Australia we have an extensive development of 

 secondary rocks and formations ranging from the oolitic to 

 the cretaceous, but these formations seem to be confined to 

 the north-east side of the continent. It is hardly likely that 

 any formations could have existed here without leaving any 

 trace, not merely of fossils, but of other changes. 



It must be admitted that this negative evidence is not con- 

 clusive. It receives a little more confirmation from the exten- 

 sive outbursts of basaltic lava which are found throughout 

 the island. These lava-flows lie either upon the carbonaceous 

 deposits, or upon drifts, or directly upon the greenstone. 

 They are of various ages, but probably not earlier than the 

 tertiary period. If there be yet any hope of finding 

 secondary formations in the island it will be underneath 

 these basalts. The tertiary lava flowing over them would 

 thus preserve them from wearing. No such deposits have 

 yet been found, as far as marine fossils are concerned, but 

 plant remains are not uncommon. This shows clearly that 

 the land was above the sea at the time of the outpouring of 

 the basalts. 



These modern volcanic rocks are nearly of similar character 

 throughout. They are black or dark blue vesicular basalts, 

 similar to what are found in New South Wales and Victoria. 

 They are almost as extensively distributed as the greenstones, 

 and are found at every altitude. They form densely wooded 

 hills on the south-east side of the island, and are more or 

 less visible in the east and north coast, on the table land, and 

 through the island, such as near Oatlands, Lake Arthur, 

 Lake St. Clair, Launceston, Table Cape, Cape Grimm, &c, 

 &c. Near Brighton a very fine section of column al basalt 

 is visible. The general character of the rock is doleritic. The 

 only specimen I ever had an opportunity of examining 

 appeared to me to show a felspathic dolerite, with triclinic 

 felspar, augite, magnetite, and either olivine or pseudo- 

 morphs, after olivine. The augite is in small brown crystals. 

 Mr. Ulrich, of Victoria, made sections of the basalt at Table 

 Cape, and found the composition to be very similar to some 

 of the recent basalts in Victoria. It was a felspar, with very 

 little augite. Vitreous quartz, magnetite, and olivine basalt 

 from Breadalbane, where there are plant remains and leaf 

 deposits, contained well-developed crystals of augite. No 



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