lxii. 



The absence of marine Older Tertiary from the eastern 

 flanks of the Cordilleras may probably be due to removal. 



The general surface of the marine beds has, however, not 

 been much affected by denudation, but the Eiver Murray has 

 cut deeply into them, leaving high yellow cliffs about one and 

 a quarter miles apart. 



Pliocene Drift or Loess. 



This remarkable formation forms the soil of the fertile 

 plains on the western slopes of the Adelaide chain, and among 

 the Northern ranges, and occupies a long strip of country of 

 a few miles in width bordering the western margin of the 

 Murray Basin. 



It everywhere presents the same general character and 

 qualities, and is doubtlessly the residuary disintegrated mate- 

 rial of the slates, limestone, gneissic, and granitic rocks of the 

 adjacent ranges. Prom the circumstance of its occurrence at 

 different altitudes in various parts of the country, as also from 

 the nature of its derivative ingredients, there can be little 

 doubt the material of each plain or flat is of local origin. 

 Among the derivative materials of the loess in the Valley of 

 the Torrens at Adelaide, I have found Miocene limestones 

 enclosing characteristic fossils, derived from the contiguous 

 cliff ; thus proving the Post-Miocene age of the formation. 

 Nevertheless, the margin of each basin is at a uniform level. 



The loess is a calcareous loam, divided into beds by irregular 

 bauds of clay or sand, which thin out at the borders, where 

 they are replaced by angular pebbles and large blocks of stone, 

 derived from the adjacent hills. The loess is very friable, yet 

 consistency is imparted to it by the presence of tubular pores, 

 branching downward like rootlets, which are lined with car- 

 bonate of lime. 



The uniformity of the surface of each plain is only inter- 

 rupted by the vertical walls between which all the members 

 of a most labyrinthine valley system are sunk. Though the drift 

 is wholly unstratified, its vertical internal structure causes it 

 to break off in any vertical plane, but in no other ; hence when 

 a cliff is undermined the loess breaks off in immense vertical 

 plates, leaving again a perpendicular wall. The rapidity with 

 which even the smallest streams cut out deep channels in it is a 

 fact that is patent to all. Channels now seA r eral yards in depth 

 and width have been eroded in a few years along the line of a 

 plough-furrow or of a dray-track. 



Another peculiarity of the loess is that it contains the 

 remains of only land animals and terrestrial vegetation. The 

 land animals are restricted to some of the extinct mammalia, 

 Diprotodon being particularly abundant in the loess of some of 

 the plains of the Northern Areas. Land mollusca have been 

 found in the loess of the Bunda Plateau, 



