58 
they extend in an easterly and westerly direction as huge, in- 
trusive masses within crystalline schists and gneisses, mostly 
devoid of vegetation, though the intruded rocks bear 
"mulga," pine tree, and undergrowth of bush and grass. 
Fertile sandy loams, carrying mulga scrub of variable extent, 
surround them ; while beyond this belt sandhills with "porcu- 
pine grass," "desert oak," "quondong," etc., prevail. 
Their main bulk consists of plutonic masses, which form 
the cores of anticlinal folds of metamorphic rocks. Owing 
to the intense metamorphism induced not only in the in- 
truded rocks, but also at the outskirts of the igneous intru- 
sions themselves, it is often impossible to determine the 
actual plane of contact. "^' This factor has further been the 
cause of the contact -rocks assuming a distinctive character by 
re-crystallisation of the original constituents (Ilornfehstruc 
tur). In this process the production of epidote has been 
greater than that of all other minerals, it being by far the 
most generally distributed near intrusions. 
The following section is a diagrammatic representation of 
the mode of occurrence of the igneous and metamorphic 
series. 
'^ X 
^ X -^ X " "v. 
rrryA x*xxvxxy,x<'''v''x'^». XXX x^x* 'oTl* ^ '^ « " < 
////x .C X "'«■*:,''**''>' X * " X ." X ^ X X X X ^ X « V V///A l>!lb^<K^l.^ 
7//^\ «XV*y X ^^ X * X " "" X ^x X XX ^„X ' ^////A<?/Ax*^x;ifV 
///v Y yXjt '<_*X)fX„x x„ ' tir^*llllln^''li:% * *« 
/77'x''-'' x^"''x^x'^«x /, x^. x\'',x :::^j U\.\\\^\ 
Fig. 1. — Diagrammatic Section through Portion of the 
MusGRAVE Ranges, East of Mitchell's Knob. 
Owing to the absence of representatives of the Cambrian 
system in proximity to the ranges, the age of the igneous in- 
trusions could not be definitely determined, but they cer- 
tainly took place before the Ordovician period, as examples 
may be seen in the low-lying outskirts, as, for instance, 
Indulkana, of rocks of the Ordovician period overlying the 
intruded fundamentals, and not being themselves penetrated 
by the eruptives. 
The Musgrave Ranges comprise an extensive series, rang- 
ing from acid to basic ; the Mann principally acid and inter- 
* Mons. Michel-Levy has described similnr features in the 
gneisses of the Central Plateau of France. He points out that 
whenever it is the case that the granite is massive and intrudes 
rocks of acid character the plane of contact is not sharp, but the 
intruded and intrusive rocks are connected by a contact zone. — 
Bull. Soc. Geol., France, Ser. 3, tonio vii. pages 852 et 853. 
