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p)Tamids of quartz are water-worn, and therefore must have existed 

 as crystals before they came into their present positions. There 

 is this pecuHarity about quartz, that whereas other minerals of a 

 definite crystalline form may be fractured, or even pounded into 

 fine dust, and yet every separate fragment will bear some definite 

 relation to the crystalline form of the original, quartz, in whatever 

 crystalline form it may be found, can never be fractured, even 

 with most skilful manipulation, into any form at all approaching 

 that of the original. We may infer from this, either that these 

 crystals represent the waste of a rock that largely consisted of 

 crystalline quartz of this form ; or else that, if the view is correct 

 that the crystalline form is due to the deposition of silica in a 

 crystalline form around a pre-existing nucleus formed by a grain of 

 sand, that part, at least, of this deposition of silica took place 

 before the rock-material settled into its present resting-place. Even 

 then we have to account for the silica. Is it possible that both 

 the silica, and part of the iron too, may have been derived from 

 Diatoms ? Their siliceous cases may easily have been dissolved 

 by the alkaline water, carried down into the lake in solution, and 

 subsequently precipitated as one of the results of the complex 

 chemical reactions there taking place. If this were the case, it 

 would help to explain much connected with the Penrith Sandstone 

 that is otherwise obscure. 



We have next to inquire in what direction this sand has travelled. 

 Everyone must have remarked the curious and somewhat puzzling 

 appearance generally presented by what looks like the stratification 

 of the Penrith Sandstone. Certain layers are clearly seen to be 

 inclined at a considerable angle in one direction or another, and 

 then just above or below these comes another set lying with 

 an angle altogether different. It is quite common for these upper 

 layers to rest directly upon the ends of the lower, just as if the 

 upper layer were unconformable to the beds beneath. Hardly any 

 of these, in this particular case, represent the true stratification, 

 but are what is called false-bedding planes, which are produced by 

 the action of strong currents of water rolling the sand forward at 

 the bottom of the lake, now in one direction and then in another 



