182 the geology of dubbo, 



4. Glossopteris Beds, Upper Coal Measures— 



With Glosso2}teris, Vertebraria, Gangamopteris. 



Origin of the Duhho Sandstone, — Having now described the 

 various appearances and the physical characteristics of the sand- 

 stones, we may proceed to enquire if any light can be thrown on 

 their origin. Mr. A . G. Green remarks in his Physical Geology 

 that if accumulations of blown sand be preserved it might be 

 difficult to distinguished them from sandstones formed beneath 

 water, unless they happened to contain land shells or land plants 

 in the position in which they grew. In one respect however, they 

 do differ. The grains are usually far more clearly rounded in 

 blown sand than in subaqueous sandstones. I may state at once 

 that the generally received opinion is that the Dubbo sandstones 

 are like in origin to the sandstones about Sydney — fresh water or 

 estuarine. I have given some attention to the matter, and excepting 

 the fact that the stratification and false bedding are not unlike the 

 stratification and false bedding exhibited in well known subaqueous 

 rocks, there is no evidence whatever to offer in support of such an 

 origin. 



Fossils are plentiful enough, but they are all land plants. They 

 are in such a wonderful state of preservation and so perfect (as 

 the members will remember from specimens exhibited at a former 

 meeting) that they could not have been drifted from any distance 

 — they must have grown where we find them. The thin seams of 

 coal represent old land surfaces. No fresh water or marine fossil 

 has ever been discovered. As far as the evidence goes, we are only 

 justified in considering the formation as Terrestrial in its origin. 



The views, and the arguments by which they are supported, of 

 the Rev. J. C. Tenison-Woods are too well known to i-equire 

 more than a reference here, but I may state that, as far as my 

 observations go, no difficulties more weighty than those already 

 urged will be furnished by the Dubbo rocks. It has been 

 suggested in Mr. Tenison-Wood's paper that were it not for 

 internal metamorphism the appearance of the sand grains would 

 afford a clue to the origin of the sandstones. Daubree, Sorby 



