334 THE DESERT SANDSTONE. 



also the fragments of crystals are much more numerous and 

 unmistakable. There is much more volcanic glass, and the gas 

 cavities have a decidedly more frothy look. Microscopic investi- 

 gation shows decided differences between the sands of the Desert 

 Sandstone and fresh volcanic sands ; but these differences are such 

 as can be accounted for by metamorphic action or local peculiarities, 

 and the resemblances are such as to show the probability of a 

 common origin. Moreover the discharge of pure creamy yellow 

 sands as ashes from certain volcanoes is an undoubted fact of 

 experience. 



Conclusion. — The following conclusions are the result of the 

 present inquiry into the nature of the Desert Sandstone : 



1. What is regarded as belonging to this formation is found in 

 detached plateaux through all tropical Australia. 



2. It is characterised on its upper surface by magnesites, but 

 the great mass of the formation is sandstone of a red, white, 

 yellow, or brown colour. 



3. Fluviatile sandstones are found near all the rivers, and only 

 near them. They are distinguished by waterworn quartz pebbles 

 and boulders which gradually increase towards the base into a 

 waterworn conglomerate. 



4. The fluviatile sandstones clip at an angle of thirty degrees 

 throughout Arnhem's Land and along the Victoria River. 



5. These sandstones are of a very broken character, rendering 

 the country in places absolutely impassable. This is especially 

 the case on the upper portion of the Daly or Katherine River. 



6. The whole of these formations, except the conglomerate are 

 probably derived from volcanic ashes. A microscopic examination 

 of the sand grains would seem to bear out this conclusion. 



7. The geological age of these sandstones is uncertain, but 

 probably belongs to the two great volcanic periods of Tertiary 

 age, the latter of which extends into the existing period. The 

 lowest beds lie upon the Cretaceous formation. 



8. The old idea of the broken edge of a great continental 

 plateau is due to this formation, which, however, exists only in 

 patches. 



9. The surface of the Desert Sandstone is not entirely sterile, 

 as it supports a poor vegetation of eucalypts, porcupine and coarse 

 grasses • but as a rule the country is of a worthless character. 



Specific gravity of Desert Sandstone. — The following table of the 

 specific gravity of specimens of sandstone collected by me was 

 kindly made at my request by Prof. A. Liversidge, F.R.S., using 

 Joly's spring balance. 



1. Red sandstone, base of Desert Sandstone, Gorge and Yam 

 Creek, 2-60. 



2. Sandstone, Victoria River, 2*51. 





