ON KAOLINITE FROM THE HAWKESBURY SANDSTONE. 177 



analyses I made by direction of the Curator of the Technological 

 Museum, upon clay from some deposits near Sydney. The first 

 a sample from Kogarah gave - 551 per cent, magnesia, and only a 

 trace of lime ; the second, from Balmain, contained -553 per cent, 

 of magnesia, but no lime ; the third, from Cornulla Beach, Port 

 Hacking, gave -640 per cent, magnesia, but no lime. Specimens 

 of these clays together with their analyses are exhibited in the 

 Museum Collection. 



An analysis is published in the Report of the Department of 

 Mines, New South Wales, for 1890, of clay from Kogarah, this 

 also gave "93 per cent, of magnesia but only a trace of lime. This 

 is sufficient to show the close relationship existing between the 

 crystallized Kaolinite and these clay deposits. 



It is probable that the Hawkesbury Sandstone has been 

 principally derived from the decomposition of granite, and the 

 large quantity of mica existing throughout assists this supposition. 

 The felspar contained magnesia, and most probably barium, as I 

 have myself succeeded in discovering barytes in this formation ;* 

 which was laid down contemporaneously with the shale beds, 

 and the sandstone. I have since traced the existence of this 

 barytes on the opposite side of Cook's River, showing its previous 

 existence across the valley. The presence of barium in felspar is 

 no new thing, and even in orthoclase and oligoclase, analyses 

 are given by Dana where ''barium is recorded. It would be well 

 in taking analyses of granite from New South Wales to be on 

 the watch for barium, it is by no means a rare mineral in this 

 colony. 



These clay deposits may eventually be proved to be kaolin, but 

 the further consideration of this subject will require to be left for 

 a later paper, as in the present state of our knowledge to attempt 

 to arrive at a decision would be premature, a searching inquiry is 

 requisite to decide the matter, as the composition cannot be 

 decided from material evidently impure. 



* Pro. Linn. Soc, N. S. Wales, Ser. 2, Vol. vi., p. 131. 

 L— October 7, 1891. 



