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is rendered comparatively easy by what is now being carried 

 on bv the Rev. J. E. Tenison-Woods, in classifying and 

 describing the organisms themselves. 



BASALTIC CAP (a.) 



It is a singular feature connected with the older stratified 

 rocks that, where exposed as cliffs, they are invariably capped 

 with sheets of igneous rock. It would seem that where 

 the soft stratified beds were unprotected by a capping 

 of this sort they have been washed away entirely or eroded 

 into valleys of which Pingal Valley may be taken as a type. 

 This supposition would fully account for the vast districts of 

 elevated table lands in Tasmania, everywhere terminating in 

 precipitous bluffs. A corresponding feature on a smaller scale 

 may be seen in connection with the stratified beds of tertiary 

 age, of which the Table Cape beds form a striking example. 

 It is probable that the deposit which forms the main subject 

 of the paper would have been entirely wasted away long ere 

 this time had it not been that during a late volcanic period it 

 was covered with sheets of basalt and basaltic tuff. The bluff 

 already mentioned is covered by a cap of basalt and basaltic 

 tuff about 80 feet in thickness. This cap, though shown in 

 diagram to be separate from corresponding caps in the neigh- 

 bourhood must have, prior to the erosion of the valleys, formed 

 with them one continuous sheet. 



The basalt at the only place where a face is exposed is greatly 

 decomposed, and at first sight it might be inferred that the 

 basaltic capping might be the re-arranged detritus of a basalt 

 older than the rock which it now reposes upon. This infer- 

 ence is however extremely improbable, inasmuch as there is 

 not the slightest evidence to show that the cap has been the 

 result of the re- distribution of older material. It may be 

 remembered that in a former paper I described a similar cap 

 of basalt, overlying the beds of lignite at Breadalbane. 



As they presented a superficial resemblance I determined 

 to subject them to analytical comparison, and for this pur- 

 pose I sent specimens of the rocks in question to Professor 

 Ulrich, of Melbourne, whose labours in connection with the 

 rocks of Australia have obtained for him a wide-world 

 reputation. After making sections of the rocks, and sub- 

 jecting them to microscopic examination he thus writes with 

 reference to the Table Cape basalt : — " The rock is somewhat 

 similar to some of our recent basalts here, viz., it is essen- 

 tially a feldspar basalt with very little augite ; lots of glass 

 and magnetic titaniferous iron, and rendered porphyritic by 

 abundant grains and crystals of olivine. It differs from the 

 basalt of Breadalbane by that the latter contains abundance 



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