56 



Certain kinds of clay beds develop these nodules of 

 barytes. In the Permo-carboniferous glacial clay at Black 

 Point, Hallett Cove, there is a layer in which a large number 

 of barytes sand-crystals occur. ( 12 ) The crystals, which have 

 incorporated sand grains in the process of crystallization, 

 form clusters that have a lenticular or subglobular shape. 



The clays of the interior of Australia in some cases carry 

 nodules of barytes. The commonest form which these con- 

 cretions take is that of a flattened cake, which has given them 

 the colloquial name of "buns." Mr. P. R. George, of the 

 Mines Department, obtained some of these baryte "buns" 

 when leader of the Government North-West Prospecting 

 Expedition in 1904. Mr. W. T. Chapman, ( 13) the assayer 

 at the Adelaide School of Mines, who analyzed one of these 

 nodules, states that "the specimens were obtained in the 

 tablelands about 50 miles west of Coward Springs railway 

 station, and occur as nodules somewhat resembling coprolites. 

 Mr. George states that the nodules vary in weight from half 

 an ounce up to about 3 lbs. They are of a grey, colour. An 

 analysis made by this department resulted as under : — 



Per cent. 

 Water 039 



Silica 



Alumina ... 

 Ferric oxide 

 Sulphuric acid 

 Baryta 

 Strontia . . . 

 Lime 



0-43 

 1-92 

 056 

 3382 

 6200 

 013 

 014 



9939 



I have recently received from Mr. George Warren, of 

 Springfield, two examples of these "buns." They were 

 obtained on the Anna Creek Run, about 60 miles to the 

 south-westward of the head station. They are known to 

 occur over an area of about 12 square miles, distributed over 

 a flat, on the northern side of a ridge of low hills consisting 

 of white clay-like rock, which is capped by a hard layer of 

 desert sandstone. The specimens are in considerable numbers, 

 and vary in size from a florin to a disk of 1 ft. in diameter. 



Whilst on a visit to Stuart Creek cattle station, in the 

 Lake Eyre district, in 1904, I came upon a white clay bank 

 that was strewn with barytes nodules of quite a different 

 shape from the "buns." They might be compared in appear- 

 ance to a ball of stout cord that had been wound and inter- 

 twined upon itself. The thickness of the cord-like casts varies 



(12) See Mawson: "Mineralogical Notes," Trans. Roy. Soc. 

 S. Austr., v. 31, 1907, p. 119. 



(13) Report School of Mines and Industries, 1904, pp. 73, 74. 



