256 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Nov. 30, 



quently the Spatangus Forbesii. At other places all organic traces 

 are lost, and the rock appears like white chalk, of an extremely friable 

 texture ; or, again, the beds appear composed entirely of Bryozoa, 

 huddled together in a very confused manner, but always forming 

 strata. The most common fossils are the PsilescJiara subsulcata (nov. 

 gen. et spec), Busk, Melicerita angustiloba (sp. n.), Busk, Gellepora 

 Gambierensis (sp. n.), Busk, which must have been, from its constant 

 recurrence, the prevailing Bryozoan of the period, several Escharw, 

 Oelleporce, Membranipora>,, Lepralice, and other Bryozoa, of which a 

 list has been drawn up by Prof. Busk, E.Gr.S., and appended to this 

 paper. Two species of Pecten also, and some Echinoderms*, are not 

 uncommon ; and casts of Univalves also occur. The only fossil which 

 I am able to identify as occurring in beds at home is the Nautilus 

 ziczac, which is frequently met with. The specimens I have sent 

 with this paper are not all equally abundant in the same strata, — 

 some prevailing more in the lower, while others are more common 

 in the upper beds. 



In a spot near Mount Gambier, where the falling in of a large cave 

 has given origin to a deep circular pit, about 100 feet wide and 90 

 deep, a complete section of the beds is exposed. It is here seen that, 

 in addition to distinct hues of stratification which occur about every 

 14 feet, there are regular zones where particular fossils are 

 associated. At the first bed (14 feet) little is seen but small 

 Bryozoa with Terebratula}. In the next (10 feet), less Bryozoa and 

 some Bivalves. The next (12 feet) is almost exclusively composed 

 of a species of Pecten, and the branched Gellepora Gambierensis. 

 The beds seem to alternate thus to the water-line (there is water at 

 the bottom of the pit), except that a Retepora ? and the Spatangus 

 Forbesii are more common lower down in the deposit. 



I cannot assert that this arrangement is found throughout the 

 district, but fossils are found in much the same way at the caves on 

 the Mosquito Plains, seventy miles distant (marked on the accom- 

 panying map), where a fine section is exposed to view. It appears 

 to me that the whole deposit has been formed in deep water, from 

 the detritus of a large reef, which may have existed at some di- 

 stance from the beds, as these appear to have been slowly spread 

 out along the sea-bottom. This would appear from the chalky 

 texture of the rock, which, when soft, must have been a white pasty 

 mass, occasionally enclosing some fragmentary fossils which had 

 escaped the general attrition. The large Gellepora Gambierensis is 

 never in an upright position, but always broken and interstratified 

 in the mass. 



The general resemblance which the whole formation bears to the 

 European Chalk is very singular. "With the exception of well-defined 

 strata and a rather more plentiful supply of fossils, the cliffs might 

 easily be mistaken for chalk-cliffs ; and then the usual sand-pipes 

 (sometimes going to great depths) and rows of flints make the resem- 

 blance most striking. The flints just mentioned are generally black, 

 occurring in regular layers, from 14 to 20 feet apart ; and one layer 

 * Mwpatagus, Echinolampas, and Clypeaster. — Ed. 



