562 



TRANSACTIONS OF SECTION C. 



that from the succeeding elevation many of the most prominent features of the 

 physiography must date. They consist of ferruginous sands, sufficiently compact 

 to stand in a vertical cliff, occasionally pebbly and false-bedded, but characterised 

 principally by the angularity of their quartz grains and the occurrence of patches 

 of kaolin and fragments of decomposed felspar. The beds contain muscovite, 

 garnet, and various iron oxides. 



Between the Cretaceous rocks and the Benin Sands two sets of sediments are 

 claimed to exist, the Ijebu Beds and the Lignite Series. Up to the present they 

 have been found only west of the Niger, though certain ill-developed sections in 

 the Eastern Province suggest that representatives of one or the other may yet be 

 found there. The beds were deposited in fresh or shallow sea-water. So far no 

 volcanic or igneous rocks have been found in any of the beds described. 



2. A7i Occurrence of Diamonds in Matrix at Oakey Creek, near Inverell, 

 New South Wales. By Professor T. W. Edgeworth David, F.R.S. 



Four diamonds were recently discovered in the matrix at the above locality by 

 Mr. A. R. Pike, after prolonged search among the doleritic and diabasic rocks of 

 the district, which he suspected to form the local matrix of the diamond. 



The spot was very carefully examined by Mr. E. F. Pittmau, Government 

 Geolo"-ist of New South Wales, who was quite convinced as to the genuineness of 

 the hnd. In fact, the internal evidence of the specimens alone is sufficient to prove 

 that the diamonds occur m situ in the igneous rock at this mine. 



A specimen of the rock containing a diamond of about half a carat in weight, 

 firmly and naturally embedded in it, was exhibited. 



The rock may be termed provisionally a hornblende-diabase. It is quite un- 

 like any of the matrix-rock of the South African diamonds, and differs from it 

 esnecially in general structure, as well as in chemical composition, as the horn- 

 blende-diabase of the Inverell district is massive, and not brecciated like the 

 volcanic rock of the diamond-bearing pipes of South Africa. 



The hornblende-diabase of Inverell occurs as a dyke 26 feet wide, cutting 

 granite probably of late Carboniferous age ; the age of the dyke is unknown, but 

 it is evidently later than the granite, and therefore post-Carboniferous. It is 

 older than the alluvial gravels at the same mine, containing stream tin and alluvial 

 diamonds. 



The following analysis of the diamond-bearing hornblende-diabase was made 

 by Mr. J. C. H. Mingaye, Analyst to the Geological Survey, Sydney: — 



ISiO^ . 

 AljO, . 



v&p., . 



FeO . 

 MgO . 

 CaO . 

 Na.,0 . 

 K,0 . 

 HjO (100° C) 

 HjO (100° C -t ) 

 CO, . 



50-43 

 14-72 

 2-90 

 4-59 

 6-67 

 7-13 

 2-47 

 1-23 

 3-82 

 3-49 

 1-67 



TiO., 



SO3 

 Cr^Oa 

 MnO 

 V..0, 



Specific Gravity -j jj' 



0-82 

 0-22 

 01 

 0-02 

 0-03 

 0-03 



100-25 



2-587 

 2-580 



Traces (less than 001 per cent ) of ZrO., 01, SrO, were found. F, S, NiO, CoO, 

 0, LijO are absent. 

 Fine silver at the r^te of 5 dwts. 10 grs. per ton. Fine gold a few grains per ton. 



In addition to the diamond embedded in the hornblende-diabase, a second 

 diamond was exhibited, which had been found at the same spot in a heap of the 

 rock, and though no longer actually in its matrix still retained small portions of 

 the base preserved in some relatively deep hollows in its surface. These cavities 

 may possibly be compared to those so frequently found in the quartz-crystals of 

 rhyolitea and quartz-porphyries, and due to the corrosive action of the base, it is, 



