213 



ULMITE, A CONSTITUENT OF BLACK SANDSTONE. 

 1!y Thos. Steel. 



At various points along the coast of New South Wales there occur frequent 

 outcrops of a black friable sandstone. The positions of some of these in the 

 Richmond River district are indicated on maps published by the New South 

 Wales Department of Mines (Ann. Kept., 1895, p. 151; 1896. "p. 155). 



At Tweed Heads a thick bed is exposed on the north bank of the river 

 near the township, from which the sample described in this paper was obtained. 

 There is no ignemi'^ rock near the deposit which is covered by a layer of or- 

 dinary sand of varying thickness. Water collected in wells dug in the over- 

 lying sand is brown in colour. 



The rock is very friable, rubbing readily l)etween the lingers to a sharp 

 sand. On ignition a fragment crumbles to loose sand and becomes white. A 

 portion heated in a glass tube yields water having a strongly acid reaction. 



Under the microscope the rock is seen to be built up of worn sandgrains of 

 fairly uniform size, each of which is covered with a thin dark-coloured film 

 resembling a coat of varnish. Gentle friction suffices to remove the coating from 

 tlie sand grains. On lixiviating the pulverised rock the dark coating can be 

 readily separated and obtained quite free from sand and, when dry, forms a 

 dark brown powder. Microscopically this shows as irregular flakes of varying 

 thickness, the thinner ones being structureless and of a translucent brown colour, 

 wliile the thick ones are black and opaque. The translucent flakes do not affect 

 polarised liglit, and, as will be shown, chemical examination proves the sub- 

 stance to consist of humus or humie acid. The powder is readily and com- 

 pletely soluble in caustic potash, soda or ammonia, forming a clear deep-brown 

 liquid which, on acidifying witli sulphuric or hydrochloric acid, deposits a 

 copious brown flocculent precipitate, leaving the solution moderately coloured. 

 In strong sulphuric ,acid the dark powder dissolves readily, particularly on 

 slightly warming, forming a clear, very dark brown solution, which, on being 

 poured into a large volume of water, throws down a copious soft brown pre- 

 cipitate, leaving the solution only slightly coloured. In strong nitric acid, the 

 powder dissolves readily, but no precipitate is produced on dilution with water 

 nor on neutralisation with alkalies. Even on boiling, the substance is only 

 sparingly soluble in .strong hydrochloric acid. 



When the precipitate obtained by dilution of the solution in strong sulphuric 

 acid is drained on a filter, the resulting slimy mass is readily soluble in water 



