85 
Watt on the Horn Expedition. These authors report* that 
Mount Watt is composed of a hard, dense quartzite, much 
fissured, and with few ferruginous bands. Fossils were ob- 
tained in the form of casts in large numbers in the quartzite. 
The exposure! examined by us is situated about six miles 
south-west of Mount Kingston, and appears in the form of 
three or four well-defined parallel ridges trending north-east- 
erly. The rock is a compact, fine-grained quartzite, in parts 
highly ferruginous. In certain zones the rock is fissile, break- 
ing into fairly large slabs from a fraction of an inch to seve- 
ral inches in thickness. The strike is E. 36' N., and dip 60° 
north-westerly. The beds are jointed in directions N.W., 
dipping 60^^ N.E., and N. 10° W., dipping easterly at a low 
angle. A ferruginous coating is found covering slickensided 
surfaces, and bands of highly ferruginous rock occur within 
the rock. A concretionary structure and dendritic precipi- 
tations of iron oxide are common. 
The outcrop appears in the midst of the desert sandstone 
tablelands, the broken outliers of which surround the 
quartzite on alm.ost every side. Its phj^sical features are, 
however, quite distinct from those of the table-top formation, 
although hand sjDecimens of the two formations may be not 
altogether dissimilar. 
The height of the exposure above sea level, by aneroid 
determination, is about 1,950 feet, and about 260 feet above 
the level of the sand. 
Mount Olga and Ayers Rock. — No doubt exists in my 
mind that Mount Olga and Ayers Rock are isolated rem- 
nants of the Ordovician system, the former consisting of a 
conglomerate, J the latter of a coarse metamorphic grit. 
These features suggest that Mount Olga was probably situat- 
ed close to the old Ordovician land surface, Mount Conner 
being distant, and Ayers Rock in a position intermediate be- 
tween the two. 
The geologists of the Horn Expedition i^ have already 
hinted at the possible Ordovician age of Mount Olga and 
Ayers Rock, while Mr. Brown, judging from specimens col- 
* Tate and Watt : Rep. Horn Expe<l. Centr. Austr., General 
Geology, page 59. 
t Mr. Wells has erected a small pile of stones on the highest 
point of this exposure. 
+ Compare W. C. Gosse, Parliamentary Paper No. 48. House 
Assembly, 1874. page 11 : — "This range is formed of a number of 
round-topped masses of solid conglomerate rock (knoAvn as pud- 
ding stone), but with stony, spinifex slopes, from 100 to 300 fee*, 
rising to their foot. Each hill is a separate rock.'' 
§ Tate and Watt : op. cit., page 59. 
