126 



€nce of living marine forms is incontestable, and the evidences 

 are in accord with those furnished by other localities on the south 

 €oast of this colony (see Trans. Eoy. Soc, vol. II., p. Ixviii.) 

 Dudley Peninsula is at the present time joined to the main 

 mass of the island by an isthmus, which at its narrowest is three- 

 fourths of a mile wide. The connecting land is low ; on the ocean 

 side the pleistocene sand-rock forms a perpendicular clifE of 

 about 40 feet high ; from the summit of the cliff the surface of 

 the ground slopes gradually inland till the shell-banks at a 

 few hundred yards from the shore at the Head of American 

 Eiver are reached. These shell-banks have an elevation of 

 from ten to fifteen feet above sea level. It has been alleged 

 that the coast about American Eiver is rising, but I am not 

 satisfied on this point. From personal observation, I have 

 no doubt that Pelican Lagoon is fast siltinjij up, and it is highly 

 probable that the appearances consequent thereon have given 

 rise to the supposition that elevatory action has taken place 

 within the last quarter of a century. The fact that Dudley 

 Peninsula has recently been joined to the other part of Kan- 

 garoo Island may have some significance when we come to con- 

 sider the origin of the flora and fauna of the island as it now is. 



SupEEFiciAL Accumulations and Soils. 



On the main portion of the island, excepting the north coast, 

 the exposures of the subter rock are rare, as it is concealed by 

 superficial debris in the form of sand, or gravelly ironstone, or 

 clays. The nature of the superficial detritus depends on the 

 nature of the subjacent rock and on relative elevation. Sands 

 largely prevail, and seem to have originated, as far as the 

 limited exposures will allow of generalization, from quartzose- 

 sandstones. Over the micaceous slaty beds ironstone gravels 

 occur on the higher ground, sand on the lower slopes, 

 whilst the basin-like depressions are levelled up with clay, 

 more or less calcareous in proportion to the amount of con- 

 tained shelly debris. In most instances the margin of the 

 inundated ground is fringed by a sheet of calcareous travertine 

 of several inches thick, derived from, and including debris of, 

 the shells of living species of Bulimcs. Not always is the 

 mollusk living over the same area, inasmuch as through lapse 

 of time the waters have acquired a too saline property for its 

 existence. The large sheet of water called Murray's Lagoon 

 is in this state ; whilst its former extension and comparative 

 freshness of its water are indicated by the considerable area 

 above present water level covered by a white chalky chiy teem- 

 ing with the shells of a species of that freshwater water-snail. 



All the above described surface deposits are of local origin, 

 and are, either from their mechanical properties or from abso- 



