266 Frederick Chapman • 



through tlie mass, generally with no definite arrangement, but 

 occasionally rudely parallel. These conditions were probably in- 

 duced by the ever-varying minor currents which would natu- 

 rally occur in the littoral or shallow-water surroundings, most 

 likelv existing during the deposition of this rock. In the friable 

 rock of the Filter Quarries may be frequently noticed a rough 

 but unmistakable structure of cross-bedding, especially where the 

 larger Lepidocyclinae are unusually abundant. 



The microscopic structure of the compact Batesford lime- 

 stone or " Moorabool Stone," as seen in thin sections, con- 

 sists of a dense mass of calcareous organisms, chiefly re- 

 ferable to foraminifera and polyzoa. There is usually very 

 little interstitial cement present, and what there is appears as 

 a fine mosaic of calcite crystals. These ciystals are also found 

 lining the cavities of the small shells. Along with the encrusta- 

 tion of these calcareous and other grains by carbonate of lime, 

 there has occurred an infiltration of iron oxide, with the result 

 that the interior of the cellular bodies is often coated with it; 

 and the structure of the fossils thereby differentiated by a thin 

 brown deposit, which in some parts definitely crystallizes out 

 as a mass of tiny rhombs, probably of the composition of 

 chalybite. In this way the chambered structure of the fora- 

 minifera is, even to the naked eye, rendered distinct, upon the 

 fractured surface of the limestone. The organisms forming the 

 bulk of the limestone, in the order of their relative abundance, 

 are Lepidocyclinae, polyzoa, Amphisteginae, Rotalia calcar, 

 echinoid spines, calcareous algae, Gypsinae and Carpenteriae ; 

 and after these only occasional examples of the rarer fora- 

 minifera, and some ostracoda. 



The fossil contents of both the friable and the compact 

 limestones are much the same ; the comparative paucity in the 

 fossil lists from the Upper Quarry being accounted for by the 

 unfavourable condition of the rock for the extraction of the 

 fossils. It is probable that in some manner this consolidation 

 of the limestone by a deposit of secondary cement is due to the 

 proximity of the granite of the Dog Rocks. Its tenacity of 

 structure and rough grain almost merits the English quarryman's 

 term " ragstone." 



Messrs. Hall and Pritchard, in the paper previously referred 

 to, state that the limestone beds show a slight dip to the S.E. 



