77 



The fossiliferous limestone in the Wilkawillina Gorge is 

 overlain by purple shales, and underlain by strong beds of 

 purple sandstone, divided by thinner beds or partings of the 

 same kind. 



XVII. LiTHOLOGic Features. 



The country dealt with in this paper supplies the most 

 extensive series of the Upper Cambrian beds that has come 

 under my observation. The lithology of the beds agrees very 

 closely with the occurrence of beds of the same age in other 

 parts of South Australia, and include quartzites, sandstones, 

 shales (or slates), limestones, and intrusive igneous rocks. 



The Quartzites are of two kinds, (a) A light-coloured, 

 very fine-grained, and siliceous rock that possesses great 

 resistance to weathering, and forms pointed and serrated 

 outcrops that* make prominent features in the landscape. A 

 rock of this kind usually underlies the Archaeocyathinae lime- 

 stones, (h) The other variety is of a dull-red or purple 

 colour, and is usually divided up into layers of a few inches, 

 or a foot or two, in thickness, separated from each other by 

 indurated shales or finely-laminated bands of quartzite. The 

 term "flaggy" has been used in the present paper to describe 

 features of this kind. 



Sandstones occur of various colours, mostly red. These 

 are especially characteristic of the eastern side of the ranges. 

 They are, usually, more or less argillaceous in composition, 

 finely-laminated, and cross-bedded, generally soft, and some- 

 times friable. They have been utilized, to some extent, as 

 flags; but are, generally, too soft for such a purpose. 



Shales (or (?) Slates). — These form the predominant 

 element in the sedimentary rocks of the district. In some 

 instances they may have developed an incipient cleavage and 

 could be called slates; but, in a general way, they are readily 

 fissile, splitting on the bedding planes, and from intimate 

 jointing break up into cuboidal fragments. As it is not always 

 an easy matter to draw a line of distinction between slates 

 and shales in the field, the term ''shale" has been adopted, 

 uniformly, for this class of rock throughout the paper. They 

 sometimes possess a greenish or drab colour, but they are pre- 

 ponderantly of a purplish tint and are, collectively, classed 

 as "purple shales." Like the quartzites and sandstones, they 

 are often divided up into definite layers of a few inches 

 thick and have the features of ''flags.'' Occasionally they 

 make prominent heights, but more commonly they weather 

 rapidly and make low ground. 



The Limestones are both numerous and of varied types. 

 Magnesia enters largely into the composition of many of 

 them. Some are true dolomites, while many others have a 



