308 THE DESERT SANDSTONE. 



to 40 feet of magnesian silicate, making a total at the highest of 

 about 270 feet above the plain. 



The coarse red sandstone lies in horizontal strata. It consists 

 of large quartz grains imbedded in a reddish-brown cement. Its 

 materials have no apparent connection with any rock visible in 

 the valley now. 



The upper stratum is a compact rock with small vesicles. It is 

 either creamy-white, yellow, or mottled a deep red-brown, with 

 streaks and veins of lighter colour. There is a concretionary 

 character about its decomposition, which makes it break up into 

 a number of small red rounded pebbles like pea iron ore. But 

 this is not always visible, only where there is much iron oxide. 

 In other places it is a pure white, and consists of a magnesian 

 silicate. The mottled character of the upper stratum is very 

 remarkable, varying through all the shades of livid red, purple, 

 yellow and brown, more in the shape of rounded clouds than 

 anything like crystallisation. No doubt it is the effect of the 

 action of water upon the iron ores contained in the ash deposits. 

 The Shackle Gorge. — The section visible near the old telegraph 

 station at Yam Creek, proceeding from above downwards into the 

 valley is as follows : — 



Magnesite ... ... ... 



Sandstone, purple and red stains . . . 



Waterworn conglomerate 



Granite ... ... ... 



130 

 In this section the magnesite is of the usual mottled and pisolitic 

 character. The sandstone is derived from granite sand of a fine 

 character, the grains being angular and not at all rounded as if 

 by eolian action. The granite is pink with very coarse felspar of 

 orthoclase and muscovite mica. It apparently belongs to the 

 great fundamental granite bed which crops out through all North 

 Australia. 



Douglas Springs. — This section is taken from the sources of the 

 Mary River in the narrow gorges of much broken tableland in 

 which that river takes its rise. 



Magnesite ... ... ... 130 feet. 



White sandstone ... ... 20 „ 



Red sandstone ... ... 50 ., 



14 feet. 



16 



55 



10 



55 



90 



55 



200 



There is no appearance of the granite formation either here or 



for some considerable distance southward. The magnesite is of 



the usual character and variously coloured, many cliffs being 



entirely white, without any red mottling. The sandstone is friable 





