THE VICTORIAN NATURALIST. 167 



is none of that peculiar stratified or tiled structure which is 

 visible at the Eveleen mine already referred to. I believe it is 

 the same formation, but I do not understand its relation to the 

 edge of the table-land with which it seems to be associated. A 

 similar formation is seen on the side of the Victoria River, with 

 large crystals of calcite. In both cases I was unable to ascertain 

 its stratigraphical position. 



Conglomerates. — Lying upon the top of the granite, and 

 underlying the desert sandstone, there are patches of con- 

 glomerate in which the pebbles are perfectly rounded and aver- 

 aging a gauge of three inches or so. There are no fossils, and 

 the formation is one due to fluviatile, and not marine action. 

 The pebbles are derived from the crystalline schists. There may 

 be some formed of granite pebbles also, but of this I cannot be 

 sure. As to its age, nothing more can be stated than that it is 

 subsequent to the intrusion of the granite, and may be as late as 

 tertiary. Since it was deposited, the granite has been cut down 

 to a depth of loo feet and more by rain and rivers. 



The base of the next formation is a conglomerate too ; and 

 they may not be distinct formations, only in some places the 

 earlier bed is completely isolated, and forms beds without sand- 

 stone, resting on the granite, about lo feet in thickness. It is 

 highly ferruginous at the base, and thus may be distinguished 

 from the quartz conglomerate in the strata above, which forms 

 large boulders and coarse gravel of milk-white colour, but com- 

 pletely water worn. 



Volcanic Rocks, Dykes, &c. — Igneous rocks are very 

 common throughout Arnhem's Land, and have played an 

 important part in the form of dykes as well as extinct craters and 

 intrusion of ancient lavas. Of the latter there is an extensive 

 outflow at the Margaret River, 114 miles south of Palmerston, 

 on the telegraph line, forming a rich tract of good agricultural 

 country. The rock is diorite, that is, a well-marked crystalline 

 and granular admixture of triclinic felspar and hornblende of 

 dark-green colour to greenish black. It forms intrusive sheets 

 rising into low ridges, with much broken stone upon the surface 

 decomposing into a reddish-brown rock. Probably this forma- 

 tion is one of the ancient trap-rocks of the country. At about 

 ten miles north of the Katherine River, on the telegraph line, 

 there is a volcanic area of several hundred square miles, with 

 very rugged hills and peaks rising to a height of four or five 

 hundred feet. I did not examine the locality closely, but I 

 encamped on a creek at the junction of the trap-rocks with the 

 edge of the limestone table-land. The rocks were tertiary, with 

 much vesicular basalt and chrysolite (olivine). A dyke of light- 

 coloured rock, like some of the altered miocene basalts of 

 Victoria, was much used by the natives for the manufacture of 



