1848.] SOMMER ON THE GEOLOGY OF WESTERN AUSTRALIA. 51 



feet in depth ; some of these remain full of water as when discovered ; 

 from others the water has been let off for the purpose of rendering 

 the cave passable. In the narrower parts or galleries, in which these 

 basins have not been formed, the bottom is covered with sand and 

 gravel of limestone and millstone grit, pebbles of various sizes, ce- 

 mented together in many places by carbonate of lime. It is unne- 

 cessary to add, that the curtain or barrier above referred to is formed 

 of layers of carbonate of lime. The temperature of the cave varies 

 very'little; the highest between November 1846 and August 1847 

 was 50° of Fahrenheit, the lowest 48°. A register-thermometer was 

 noted and left in the Pillar Hall (b) in the former month and again 

 observed in the latter. The total length measured along the middle 

 of the cave is 702 yards. 



4. A Sketch of the Geological Formation and Physical Structure of 

 Western Australia. By Ferd. von Sommer, Dr. Med. and 



Phil. 



[Communicated by the Secretary.] 



Dr. Sommer states that he was charged by the Local Government 

 of Western Australia to examine and to trace out a seam of coal found 

 by accident about a year ago in the bed of a creek or temporary river 

 called the '' Irwin," at a distance of 200 miles northwards from Perth. 

 He begins his description with Port Grey, or as the northern divi- 

 sion of that diluvial segment is called. Champion Bay. Both divi- 

 sions or bays are separated and in a great measure formed by a small 

 peninsula of two miles in length and three-quarters of a mile in 

 breadth, stretching nearly from east to west ; composed of a peculiar 

 kind of oolitic limestone of combined coral and shell formation and 

 covered with sand. The older parts of the line of coast in this neigh- 

 bourhood, as well as the islands of a corresponding age, rest on a more 

 crystalline secondary limestone. The newer portions of the coast, 

 with the long reefs which shelter the bay against north-west gales, 

 and the numerous groups of low islands, called the Abrolhos, are 

 composed of a softer oolite resting on compact, often crystalline coral. 

 The same marine agent operates still, as well in forming new bays 

 and islands as in shutting up old bays (converting them first into 

 estuaries and then into diluvial soil), and in shutting up the rivers 

 of Western Australia with bars. 



These new diluvial formations are materially assisted by hills of 

 quicksand driven by wind and waves over the reefs and bars often 

 to the height of some hundred feet, as is to be seen at the estuary of 

 the Hutt, Champion Bay, and Jurieu Bay. These sand-downs are 

 then often cemented with a pasty solution of softer shells, and are 

 soon covered with a sahferous vegetation forming the foundation of a 

 new country. 



These well-known contemporary modifications of the sea-boundary 

 are perhaps nowhere more obviously manifested. The estuary of the 

 Hutt, for instance, is, since the few years when it was first seen by 

 Capt. Grey, already so much altered that Dr. Sommer could scarcely 



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