184 



THE GEOLOGY OP DUBBO, 



to plates of mica which are visible on the fresh surfaces. Wind 

 could not induce such a structure, unless the sand and mica were 

 drifted into quiet water. This is exceptional, and very different 

 from the greater part of the rock, where the mica is uniformly 

 and sparsely distributed throughout the mass. 



Rich th of en describes a wind blown deposit (unstratified) in 

 China, more than 1500 feet in thickness. He refers this to an 

 origin wholly seolian, and calls it by the name of land-loess, to 

 distinguish it from like deposits in which water has co-operated. 

 The latter he calls lake-loess. I consider the sandstones at Dubbo to 

 be a lake-loess formation. Further research may find material for 

 another view, but with the materials in hand it would hardly l)e 

 justifiable to come to any other conclusion. 



I may here observe that in the discussion on Mr. Tenison- Wood's 

 paper, mention was made of recognising hyalite in thin slices of the 

 rock. I have succeeded in preparing a few sections, which I now 

 exhibit. The cohesion between the particles is, as a rule, so slight, 

 that sections cannot be prepared except where metamorphism has 

 more than ordinarily affected the rock. Unfortunately these sections 

 give us no idea of the original structure. In the sections I lay 

 before you the partly formed crystals as are close as the constituents 

 of a ternary granite. 



Origin of the Ironstones. — Beds of Ironstone are found at various 

 levels in the series, but not to any considerable extent, except 

 on the Talbragar River up and down from Ballimore. At the last 

 named place (vide section above) it occurs in beds and lenticular 

 masses, which leave no doubt as to its origin. It would be hard 

 to find a better example than Ballimore, to illustrate the process so 

 clearly put by Dr. S. Hunt in his " Origin of Metalliferous 

 Deposits " (Chem. and Geol. Essays, p. 228). Every bed of iron- 

 stone marks an old surface as surely as every coal bed does. The 

 bands of ironstone, never more than a few feet thick, represent 

 shallow " lagoons" which held ferruginous water, derived from the 

 surrounding rocks, through the agency of decaying organic matter. 

 It might be said that eveiy bed of iron represents a bed of coal. 



