THE DESERT SANDSTONE. 305 



preservation in a way which I shall try to explain hereafter. Yet 

 it may also be inferred that the absence from other places may be 

 more apparent than real. An attentive examination has not been 

 made, or these ash remains would possibly have been much more 

 extensively recognised. It must be borne in mind that Mr. Jack 

 the Government Geologist of Queensland, and myself have been 

 the only geologists who have paid attention to the matter, and 

 attributed to these strata their true character. I may say, however 

 with some confidence, that though few ash beds have been recorded 

 as occurring on the south of the Australian continent, unless in 

 seams that are quite insignificant, it is only because the true 

 nature of such formations has not been understood. In the "Notes 

 on the Physical Geography, Geology and Mineralogy of Victoria"* 

 (p. 74) Messrs. Selwyn and Ulrich, report many important deposits 

 of magnesite, thus : — " Magnesite (Carbonate of Magnesia) — This 

 mineral is tolerably abundant in the 'kaolin' deposit of Bulla 

 Bulla, near Keilor, at Heathcote, and generally in the Tertiary 

 clays near Geelong, Bacchus Marsh, Western Port, <fcc. ; also in 

 the surface soil along the banks of the Lodclon River, near 

 Newstead, forming nodules of all shapes and sizes, from that of a 

 pea to several inches cubic. According to analysis these nodules 

 are however, not composed of pure carbonate of magnesia, but 

 contain small variable proportions of carbonate of lime, carbonate 

 of iron, and clayey matter. A peculiar occurrence of very pure 

 magnesia is observable at the Hard Hills, near the junction of 

 Jim Crow Creek and the Loddon River. It appears like an 

 annular outcrop of a bed of nearly one foot in thickness round the 

 base of a small hillock, composed of older Pliocene gold drift, but 

 extends barely a few inches beneath the surface. This outcrop 

 consists of an aggregation of nodules of all sizes, from several inches 

 diameter to even fine roundish grains, like oolitic sand. Some of 

 the nodules are extremely hard and homogeneous, but the generality 

 consist of roundish particles of pea-size, with obscure rhombohedral 

 planes, sometimes closely, but in most cases very loosely adhering 

 together. The origin of the mineral appears to be due to the action 

 of the carbonic acid of the atmosphere on a seam of white soapy 

 clay which contains a large percentage of silicate, and perhaps 

 hydrate of magnesia, and would crop out now where the raa^mmte 

 appears. Where the atmosphere could have no access to the clay, 

 there is a total absence of magnesite, whilst on the other hand, in 

 places where the clay has been exposed to its influence, even in 

 the most recent times — for instance in the drift heaps from several 

 shafts on the hillock — the small white grains appear in profusion 

 like white sand artificially strewn over the surface." 



* Intercolonial Exhibition Essays, Melbourne, 1866. 

 T— November 7, 1888. 



