82. 
whole, shows no signs of bedding, but the impurer portions 
(siliceous) exnioit faintly planes of deposition and current 
bedding that are rendered more apparent on partial denuda- 
tion of the rock. The character of the rock varies from a 
bluish, sub-crystalline limestone to a granular marble, to be 
in parts replaced (in the upper layers) by coloured siliceous 
and dolomitic limestones. The crystalline limestone con- 
tains accessory minerals, as small, perfect crystals of fiuorite 
and aggregates of ankerite, while carbonates of copper occur 
as locally concentrated fissure fillings and pockets of incon- 
siderable magnitude or quality. Chert nodules that have 
possibly been derived from solution of contained radiolarian 
tests, or enclose the spicules of Cambrian sponges."^ weather 
from the surface of the limestone, by virtue of their superior 
hardness. They are flattish-ovoid in shape, and are bounded 
by regularly curved, smooth surfaces. 
Ordovician. 
Exposures of beds of the Ordovician period were met 
with in districts widely separated from one another, namely, 
at Indulkana, Mount Conner, and the Mount Kingston out- 
crop. 
Indulkana. — Mr. H. Y. L. Brown visited this outcrop 
in 1889, and reported! similar rocks to extend in a direction 
southward to Arcoollina Well, and for a long distance west- 
wards. Mr. V. Streich passed the same outcrops two years 
later,! and traced the western boundary of the same forma- 
tion to Townsend Ridge, over one hundred miles beyond the 
border line of Western Australia. 
On approaching the Mount Chandler range from the 
north, it has the appearance of a tableland, with its surface 
sloping slightly westward. This is not, strictly speaking, 
the case, for, on entering the range, it is found to consist of 
a series of parallel ridges trending from east to west. The 
whole formation at this locality appears in the form of a 
shallow, synclinal trough, the axis of which pitches 
east and west. The strike of the beds is E. 
5° S. The rock is composed principally of a 
* Since writing this paper Mr. R. Etheridge, jun., of Syd- 
ney, has kindly examined a section of one of the.se nodules for 
me. He writes tliat, 'tlu^ micro-section of the nodule appears to 
consist of calcite and chalcedony, with perhaps a third undeter- 
mined mineral. I cannot distinguish any trace of organic struc- 
ture." 
t H. Y. li. Brown : Kepoi't on Journey from Warrina to Mns- 
grave Ranges (by authority: Adelaide, 1889). 
: V. Streich: Scien. Hes. Elder Expl. l^^xped., 1891-2, Geo- 
logy. Trans. Roy. Soc, S.A., vol. xvi., page 80. 
