THE DESERT SANDSTONE. 325 



I have taken it for granted here that the Desert Sandstone in 

 North Australia is of Tertiary age. This assumption depends upon 

 the fact of its strong resemblance to a similar formation in 

 Queensland which rests upon Cretaceous rocks. It is worth while 

 however, to warn observers that the nature of such formations, 

 that is simple sandstones without fossils, is to resemble each other 

 as closely as possible, no matter to what age they belong. It is 

 quite possible that sandstones of the middle or lower Mesozoic 

 might be mistaken for those of Queensland, and therefore I do 

 not assert positively that those we have been treating of are 

 Tertiary, much less to claim for them any place in the Tertiary 

 system. Yet it must be added that the recent character of the 

 basalts and dolerites cannot be doubted, and all geologists have 

 regarded them as Pliocene. The Mesozoic volcanic products on 

 the other hand are diorites or greenstones of very uniform character 

 throughout Australia and Tasmania. 



It is unnecessary to describe all the localities where I have 

 collected sands as I have given details of the microscopic 

 appearances presented. It has already been stated that the 

 volcanic rocks form more or less a ring round the northern, 

 eastern, and part of the southern sides of the Australian continent. 

 My observations have convinced me that the volcanic period has 

 altered the physical features of the eastern side of the continent 

 in a remarkable manner. Wherever recent lavas occur they now 

 form the watershed between the rivers flowing into the Pacific Ocean 

 and those flowing westward into the interior. Before this volcanic 

 period the Divide on the eastern side was mostly granitic, and 

 even now forms a much higher portion of the mountain range. 

 The trap-rocks always give rise to rivers, some of which are 

 amongst the most important on the north and east coast, such as 

 the Flinders, the Victoria, the Leichhardt, the Roper, the Daly, 

 the Mitchell, (fee, &c. There arises also another set of rivers of 

 smaller dimensions having their sources in the springs at the edge 

 of the Desert Sandstone. 



It can be proved however, that there has been formerly a very 

 gradual slope from the ocean towards the centre of the continent, 

 and that what is called the plateau is a local accumulation of 

 limited extent. Yet some of the extinct craters are so far inland 

 that it would be hard to restrict the boundaries of the ash and lava 

 strata. They may be found in patches right through the continent. 

 To suppose that they once occupied a very much larger area, or 

 covered the whole country seems from the nature of the case 

 to be an exaggerated view. Volcanic sands may have been carried 

 to great distances, but until observation has shown that they 

 covered the whole continent, we are hardly justified in supposing 

 it. The frequent recurrence of the sandstones in widely separated 



