44 



Rocks 1 to 4 are all more or less unconformable to each, 

 other, and they abut against the granite axis on the eastern and 

 western sides. 



THE HELICID^ SANDSTONE. 



This formation is of particular interest. It is found upon 

 nearly all the islands iip to a height of 100 feet, and for 

 the most part it lies directly upon the granite. It varies in 

 character from a coarse gritty sandstone, with minute worn 

 fragments of marine shells, to a close-grained cherty or 

 arenaceous limestone. It is found on Barren Island, forming 

 a more or less precipitous coast line of horizontal strata, at 

 intervals, between a j^oint opposite Doughboy Island and 

 Thunder and Lightning Bay. On Badger, Chappell, G-reen, 

 and Kangaroo islands it is the prevailing rock, ancl invariably 

 is found to lie directly upon granite or the upturned edges 

 of mica-schist rock. The weathered portions present a 

 curiously rough and honeycombed api:)earance, and frequently 

 give out a sonorous metallic tone when struck by the 

 hammer. 



The most characteristic feature, however, is the imbedded 

 remains of various species of HeVicidcE, together with certain 

 species of Siiccmea. In certain layers of calcareous clay — 

 evidently the sediment of some ancient brackish lagoons — 

 occurs a species of BiiliyneJla in the greatest abundance. I 

 believe the shell to be closely allied to the existing fresh, 

 water shell, B. Jegrandi. 



In some places the remains of two small species of Helix 

 seem to compose 20 per cent, of the mass of the rock. They 

 are very similar to sjjecies now fomid in myriads in the 

 shallow hollows filled with dead leaves in the drift sand of 

 the dunes now forming. In communicating these facts to 

 Professor Ralph Tate, he replied that " in the S.E. coast of 

 this colony (South Australia) — and particularly I noted that 

 the sandstones of Cape Northumberland (100 feet or more 

 in height), were consolidated blown sand ; in them I found 

 two species of Helices. The tv>'0 species of Helices from Cape 

 Northumberland (Ijoth occur living on the spot) are among 

 those you sent me." 



It is, therefore, of much interest to find that the sand 

 dunes, consolidated, enclosing certain species of Helix, should 

 have such a wide range. In a dried-up lagoon, evidently of 

 more recent date than the sand dunes, I found a species of 

 PJiysa, and a species of Pomatio2)sis, or Blanfordia. Of 

 these and the other shells found in the consolidated sand 

 dunes Professor Tate makes the following observations : — 



