78 
Lying between these masses, disconnected, rounded hills 
of metamorphic rock appear, rising, as in previous instances, 
from a vast expanse of sand. 
Igneous 7j'oc*A-.s.--The granite is somewhat coarsely crys- 
talline, normal to slightly porphyritic, the felspar often oc- 
curring as porphyritic individuals. Magnetic ores of iron 
are plentifully developed. The rock is superficially rotten. 
The mass shows typical granitic features, with a regular, ver- 
tical system of jointing, which sometimes, by weathering, 
have formed large caves, notably north-west of Mount Cave- 
nagh. The intrusion appears to have occurred in a direction 
north of west, and the Mount Cavenagh outcrop is divided 
by a series of parallel gullies running in a northerly direc- 
tion. Outcrops of identical rock were found intermediate in 
position between Mount Sir Henry and Mount Carnarvon, 
thus geologically connecting the Musgrave and Ayers Ranges. 
About fifteen miles south of Mount Cavanagh a different 
type of granite is found adjacent to a belt of dioritic intru- 
sion. It is a highly felspathic graphic granite, the felspar 
being a light red orthoclase, and in parts is pegmatitic. Fur- 
ther east it has suffered considerable metamorphism, and is 
veined by saussuritic rock and a coarsely crystalline, fels- 
pathic, acid modification. 
Diorite intrusions are exceedingly plentiful. The south- 
ern extremity of the ranges is a pronounced ridge, rising about 
200 feet above the plain, about a mile wide, and extending 
for several miles east and west. It is composed almost en- 
tirely of diorite intrusions, with the exception of a few "float- 
ing" masses of highly altered rock in the same. The dykes 
trend within a degree or two of due west, and are either reju- 
larly jointed into quadrangular blocks or weather into round- 
ed masses resembling granitic tors. Between this prominent 
ridge and Mount Sir Henry a marked series of parallel diorite 
dykes, usually of no great thickness, continues for nearly the 
whole distance, a dyke being met with at every few chains. 
Their direction is east and west, with very few exceptions. 
A few low exposures of the bedrock were met with, consist- 
ing of various modifications of altered granite. 
Metamorphic Rorhs. — The gneiss has its greatest develop- 
ment in the east of the ranges, occurring as more or less iso- 
lated bare hillocks. It is linearly foliated, the planes of foli- 
ation striking N. 10° E., and dipping W. at Kurrekapinnya 
soakage. This fact seems extraordinary, as in all other cases 
noted the foliation of the gneiss coincided in direction with 
the trend of the intrusion, and this evidence, in conjunction 
with other physical features, has suggested a change in the 
direction of intrusion of the granite. The rock is jointed in 
