10 



stratification which, in the case of the concretions, pass out into the 

 shales in which they are imbedded. There is no doubt of their being 

 formed in situ although an opinion has been expressed to the con- 

 trary the hardening being produced by the organic acids in the 

 animal and plant remains acting on the ferruginous constituents 

 of the shales. Iron pyrites is of frequent occurrence, and some of the 

 fossil fish and insects have been preserved in this mineral. Fossils 

 are occasionally found which are not encased in the concretionary 

 clay ironstone, but in such cases the matrix of shale is generally more 

 or less sandy and porous, allowing free percolation of mineral solu- 

 tions, and consequently with less precipitation of mineral matter 

 around the fossils. One could tell fairly well by appearances if a 

 concretion contained shells, leaf fragments, fish remains, or nothing 

 at all, those containing the fish almost always conforming with the 

 shape of the individual, and having a somewhat concave depression 

 above, and a gentle convexity below. 



The Unios were always found in roughly spherical concretions, 

 generally congregated around an axis of wood which must have 

 been partly decayed before fossilization, the insects being found in 

 concretions in association with both fossil fishes and Unios. 



The shales containing the fossil remains insects, fishes, laby- 

 rinthodonts, coprolitic fragments, and plants belong to the Wiana- 

 matta shales, a series probably equivalent to the Upper Clarence 

 Series in Northern New South Wales and the Darling Downs-Walloon 

 Coal Series in Southern Queensland. This position for the St. Peter's 

 fossil beds places the horizon in the Jurassic and above the fossil 

 bed at Ipswich, which is probably Upper Triassic. 



