148 New South Wales. paet l 



morphic action, I was surprised at observing that, in 

 some specimens, nearly all the grains of quartz were so 

 perfectly crystallised with brilliant facets that they 

 evidently had not in their present form been asrsrearated 



J JL O O O 



in any previously existing rock. 1 It is difficult to 

 imagine how these crystals could have been formed ; 

 one can hardly believe that they were separately pre- 

 cipitated in their present crystallised state. Is it 

 possible that rounded grains of quartz may have been 

 acted on bv a fluid corroding: their surfaces, and de- 

 positing on them fresh silica ? I may remark that, in 

 the sandstone formation of the Cape of Good Hope, it 

 is evident that silica has been profusely deposited from 

 aqueous solution. 



In several parts of the sandstone I noticed patches 

 of shale which might at the first glance have been 

 mistaken for extraneous fragments ; their horizontal 

 laminae, however, being parallel with those of the 

 sandstone, showed that they were the remnants of thin, 

 continuous beds. One such fragment (probably the 

 section of a long narrow strip) seen in the face of a cliff, 

 was of greater vertical thickness than breadth, which 

 proves that this bed of shale must have been in some 

 slight degree consolidated, after having been deposited, 

 and before being worn away by the currents. Each 

 patch of the shale shows, also, how slowly many of the 

 successive layers of sandstone were deposited. These 

 pseudo-fragments of shale will perhaps explain, in some 

 cases, the origin of apparently extraneous fragments in 



1 I have lately seen, in a paper by Smith (the father of English 

 geologists), in the ' Magazine of Natural History,' that the grains of 

 quartz in the millstone grit of England are often crystallised. Sir 

 David Brewster, in a paper read before the British Association, 1840, 

 states, that in old decomposed glass, the silex and metals separate 

 into concentric rings, and that the silex regains its crystalline struc- 

 ture, as is shown by its action 00 light. 



