THE VICTORIAN NATURALIST. 171 



are of white quartz, of which, strange to say, there are no veins 

 in the porphyry rock. This sandstone forms table-lands on both 

 sides of the Katherine River a mile, or two in width, for some 

 miles. Then the metalliferous slates succeed, with tin and 

 alluvial gold. The fluviatile sandstone formation is much broken 

 into immense boulders, and rocks of most fantastic shapes. It 

 is very hard, but being full of cracks and fissures, it weathers 

 easily, and gives rise to an exceedingly rough and almost 

 inaccessible country. It is composed of sandbanks and river 

 boulders which have hardened since the rivers cut through 

 them. 



The formation dips away to the east along the existing streams 

 at an angle of about 30 degrees. Mount Douglas will afford an 

 illustration of this. It is a castellated hill, quite abrupt on its 

 south-western end, and showing in section 400 ft. to 500 ft. of 

 these fluviatile conglomerates. It forms the extreme end of 

 ranges of very broken meridional hills not exceeding 500 ft. in 

 height. The strata dip away from the River Mackinlay at an 

 angle of 30 degrees, possibly representing the direction of the 

 currents wherein the conglomerates were formed. I have 

 noticed a similar dip at the Margaret River, Kekwick's Springs, 

 near the head of the Mary, and at the Katherine and Victoria 

 Rivers. This uniform dip, its hard flaggy nature, and the 

 included waterworn pebbles, are unmistakable characters of this 

 formation. 



These conglomerates have probably been derived from a river 

 channel through the paleozoic rocks, which contain an abundance 

 of quartz reefs. The sand has been an ash deposit fiUing up the 

 channel and mingling with or covering up the conglomerate, 

 which generally increases toAvards the base of the formation, to 

 the exclusion of the sandstone. This formation does not differ 

 essentially from what are called the " drifts " of Victoria and 

 other colonies. 



Desert Sandstone. — This peculiar formation varies" much in 

 colour and character, though mostly of a bright and livid red, yet 

 it is often white, yellow, mottled, &c. It is usually composed 

 of small, somewhat rounded sand grains, though in some places 

 there are admixtures of magnesite, carbonate of magnesia, &c. 

 It gives rise to a desert country with scanty vegetation, is 

 generally destitute of fossils, and is of a broken, precipitous 

 cliaracter, forming table lands with precipitous faces, and round, 

 flat-topped hills. It is nearly always of uniform height, and is 

 probably underlain throughout Arnhem's Land by the crystalline 

 schists. Mr. Daintree, who named the formation " desert sand- 

 stone," was of opinion that it at one time covered the whole 

 continent ; but my own observations and microscopic examina- 

 tion of the sands have led me to conclude that it is derived from 



