Geology of the Loiver Mitchell River. 39 



sediments, as practically contemporaneous, that is, they belong to 

 the same horizon of the eocene. It is true that both at Dreir's 

 and Skinner's, the calcareous shell beds underlie the Bairnsdale 

 limestone, and must therefore have been first laid down, but at 

 Boggy Creek the ironstones of the amphitheatre, in which similar 

 fossils are now represented by casts, actually overlie the same 

 limestones. Those who have studied the marine tertiaries of 

 Southern Australia, will doubtless recall somewhat analogous 

 occurrences in the eocene of other localities. The relationship 

 of certain well-known calcareous or clay beds, with a rich 

 assemblage of fossils, to adjoining polyzoal limestone has been 

 discussed in various memoirs, and it will suffice to say here that 

 their close palaeontological affinities are now generally recognized. 

 The proximity of the former shore line renders the solution of 

 the problem for the Mitchell sections comparatively easy. The 

 creeks or rivers which discharged into the eocene sea would 

 bring down sands and clays, and a favourable matrix for the 

 preservation of the tests of gastropods, corals, etc., would thus 

 exist, while in the quiet clear waters of areas removed from the 

 action of such currents, the faunal remains might at the same 

 time accumulate as beds of limestone. In the latter, oysters, some 

 species of pectens, echinoderms, etc., are usually more abundant 

 than in the clays, while univalve moilusca are comparatively 

 scarce. The preponderance of certain fossil forms in the 

 respective strata may probably be accounted for by the nature 

 of the enclosing media. Though the large majority remain intact 

 oidy in the clays and calcareous sediments, a few are certainly 

 best preserved in the limestones. Attention may here be called 

 to Mr. F. W. Harmer's description of the Coralline Crag of 

 Suffolk (England), wherein he states that pectens and other 

 moilusca with calcitic tests, and the remains of bryozoa are 

 common, but the opaque or ai'agonitic moilusca are represented 

 by casts only\ 



Similar remarks are applicable to the Bairnsdale limestones. 

 In some portions of the latter, as at Swan Reach (5), casts of 

 gastropods, though not plentiful, yet occur, but they are rarely 

 identifiable. 



2 Q.J.G.S., vol. liv., p. 321. 



