THE DESERT SANDSTONE. 303 



Before dealing in detail with these different formations, it is 

 important to point out a fact which has a significant bearing on 

 their origin. If a geological map of any portion of the interior 

 is consulted, it will be observed that in many instances where 

 recent volcani rocks are marked, they are seen to be associated 

 with what is called the Desert Sandstone. Sometimes, as at 

 Dubbo, Wellington, War-burton, Sofala, &c, it is called 

 Hawkesbury Sandstone, but the connection with the volcanic 

 rocks is indisputable. The position that these sandstones always 

 occupy with reference to the points of ejection of the recent 

 volcanic rocks, shows that they are dependent upon them, and 

 they are sometimes intercalated with them as I shall show 

 hereafter. The high lands of New England, which contain large 

 manifestations of recent volcanic rocks, are rich in these sandstones 

 too, which the late Mr. Lamont, one of the able assistants of 

 Mr. Wilkinson in the geological survey, early recognised as 

 ash-beds. In the interior on the Lachlan, Darling, and the back 

 country between both, there are many instances of Desert 

 Sandstone occurring as detached outliers, but always so near 

 recent volcanic rocks that they cannot be otherwise than connected 

 with them. Particular instances of this will be given further on, 

 but it is important to note the facts themselves at this stage of 

 the paper. 



I will now proceed to give detailed descriptions of the various 

 formations in the Desert Sandstone which I have enumerated 

 above. 



Magnesite deposits — I venture to suggest that we have in these 

 strata remains of a volcanic origin which have accumulated 

 during a long period of volcanic activity. The beds seem to 

 have occupied a wider area than they do now. They vary in 

 thickness from 10 feet to 500 or even more, though the thickest 

 deposits measured by me did not exceed 40 feet. They are now 

 formed into a compact and various coloured stone, consolidated 

 no doubt by chemical action and decomposition as well as pressure. 

 If my suggestion as to the volcanic orgin of these magnesite 

 beds be accepted, we have not very far to seek for volcanic points 

 of ejection, from which they may have proceeded. Geological 

 readers need scarcely be reminded of the great mass of trap-rocks 

 which encircles the edge of the continent of Australia, with 

 perhaps the exception of the south-west side. Western Victoria 

 seems one of the recent foci of activity, the latest disturbances 

 having occurred at no great distance from the mouth of the river 

 Murray. Very recent outbursts have also occurred about the 

 middle of the east coast, in the latitude of Moreton Bay, where 

 volcanic emanations and existing shells are mingled together on 

 the coast. It is difficult to form an opinion as to the relative 



