306 THE DESERT SANDSTONE. 



I have very little doubt that in many of the places here 

 enumerated, the magnesite is derived from volcanic ash, probably 

 in a decomposed condition. The deposit observed at Hard Hills 

 on the Loddon River belongs to the great volcanic outbreak, which 

 has covered the country with basalt more or less uninterruptedly 

 all over Western Victoria, and which includes a large number of 

 extinct volcanoes. 



Prof. Liversidge in his "Minerals of New South Wales, "* thus 

 speaks of magnesite (p. 165): — It is found in New England in 

 various places, and upon the diamond fields at Bingera, co. 

 Murchison (where the mineral has a peculiar reticulated surface 

 and mammilated form) and near Mudgee. When impure it is of a 

 grey or grey-brown colour, but when pure it is a dazzling white, 

 compact, tough, and breaks with a flat conchoidal fracture. . . 

 Other localities are Kempsey; Mooby Gully, Lachlan River ; Scone 

 co. Brisbane; Louisa Creek and Lewis Ponds Creek, co. Wellington; 

 Barabba, co. Darling ; Tumut ; Gulgong ; and Warrell Creek, 

 Nambuccra River. 



We might include also to some extent serpentines as well as 

 magnesites, though I have not met with any such deposits of an 

 extensive character that seemed attributable to volcanic ash. 



One of the main sources of the magnesium salts would be 

 doubtless from volcanic rocks, and particularly basalts containing 

 olivine. By many of the older mineralogists only those volcanic 

 rocks which contained olivine were regarded as true basalts : at 

 any rate basalts containing large quantities of olivine are extremely 

 common. Thus Messrs. Selwyn and Ulrich, in the work already 

 referred to, state under the head of olivine or chrysolite (op. cit. p. 

 66) that " this mineral is so common in the newer basalts (except 

 where the latter appear as true ' dolerites ; ) as to deserve to be 

 regarded as an essential constituent of the rock. It generally 

 appears disseminated in small angular grains of light apple to 

 blackish-green colour ; but at many places, especially in the 

 neighbourhood of basaltic craters and points of eruption (Mount 

 Franklin, the Anakies, Gisborne Hill, the Warrion Hills, &c.) it 

 occurs in irregularly shaped, or sometimes spheroidal masses, of 

 both fine and coarsely granulated texture, and from one to five, 

 in some instances (Anakies) to even twelve and eighteen inches in 

 diameter. Crystals have not been observed as yet. An analysis 

 by Mr. Daintree of light green olivine from the Anakies yielded : — 

 Silica ... ■ ... ... ... 42-60 



Protoxide of iron... ... ... 7*36 



Magnesia .... ... ... 50*00 



99-96 



* London, Trubner & Co., Ludgate Hill, 1888. 



