192 



much is yet to be learnt of the fossil contents of this form- 

 ation, still the list is of a sufficiently complete nature to 

 enable a comparison to be made. 



The Wandrawandian Series is perhaps the richest in 

 fossils in the Shoalhaven district, and from them comes 

 most of the material which is here dealt with. Burrier 

 was the most profitable locality, and from here within a 

 short distance, 42 species have already been obtained. At 

 Grassy Gully also a good variety occurs, and here 16 

 species were procured. 



The vertical range of species in the Permo-Carboniferous 

 formation is a most important subject, which has as yet 

 been but little touched upon. Unfortunately but little 

 comparison can be made with the Upper Marine Series in 

 the Maitlaiid District, for the various horizons there, 

 though definite, nevertheless have been laid down under 

 very different conditions to those in the south, the local 

 geography having in each case been at that time essentially 



Great care must be taken in the division of sedimentary 

 formations into horizons by their fossil contents alone, for 

 it is necessary, not only to observe the difference, but to 

 ascertain how much of it is actually due to the natural 

 extinction of old with the development of new species, 

 and how much is merely caused by a redistribution of 

 species due to changes in conditions, the one series 

 migrating to new habitats, and the other arriving from 

 neighbouring areas to take its place. This is exemplified 

 in the Wandrawandian Series from Yalwal Creek to Burrier, 

 where along one horizon, a complete change in fauna takes 

 place due to local conditions. So that working on fossil 

 evidence alone, the rocks at Yalwal Creek, Grassy Gully 

 and Barrier would seem to belong to entirely different 

 formations. 



