chap. vn. Sandstone Platforms. 147 



crystals of quartz, and intersected in some places by 

 trap-dikes. Near the Downs of Bathurst I passed over 

 much pale-brown, glossy clay-slate, with the shattered 

 laniinge running north and south : I mention this fact, 

 because Captain King informs me that, in the country 

 a hundred miles southward, near Lake George, the 

 mica-slate ranges so invariably north and south that 

 the inhabitants take advantage of it in finding their 

 way through the forests. 



The sandstone of the Blue Mountains is at least 

 1,200 feet thick, and in some parts is apparently of 

 greater thickness ; it consists of small grains of quartz, 

 cemented by white earthy matter, and it abounds with 

 ferruginous veins. The lower beds sometimes alternate 

 with shales and coal : at Wolgan I found in carbona- 

 ceous shale leaves of the Glossopteris JBrownii, a fern 

 which so frequently accompanies the coal of Australia. 

 The sandstone contains pebbles of quartz ; and these 

 generally increase in number and size (seldom, however, 

 exceeding an inch or two in diameter) in the upper 

 beds : I observed a similar circumstance in the grand 

 sandstone formation at the Cape of Good Hope, On 

 the South American coast, where tertiary aud supra- 

 tertiary beds have been extensively elevated, I re- 

 peatedly noticed that the uppermost beds were formed 

 of coarser materials than the lower : this appears to 

 indicate that, as the sea became shallower, the force of 

 the waves or currents increased. On the lower plat- 

 form,, however, between the Blue Mountains and the 

 coast, I observed that the upper beds of the sandstone 

 frequently passed into argillaceous shale, — the effect, 

 probably, of this lower space having been protected 

 from strong currents during its elevation. The sand- 

 stone of the Blue Mountains evidently having been of 

 mechanical origin, and not having suffered any meta- 



