348 T, G. TAYLOR AND D. MAWSON. 
in containing a blue hornblende allied to arfvedsonite. The 
main point of distinction being that the Mittagong variety 
is more even grained and compact. 
There has been much speculation by geologists of this 
State as to the relations of the igneous magmas, and their 
positions in the Permo-Carboniferous coal basin of eastern 
New South Wales. Much work’ has already been done in 
this connection, chiefly by the Geological Survey Depart- 
ment, and it is hoped that this paper will form one more 
link in the chain of evidence needed, before evidence is no 
longer supposititious, and theories become facts. 
The igneous rocks of the Mittagong district form only 
one example of volcanic activity subsequent to the depo- 
sition of the sedimentary rocks in this coal basin. Many 
more have already been described, chiefly constituting 
extensive flows of basalt and associated dykes met with 
over a large portion of the area. 
Attention has already been drawn to the fact that the 
more acid rocks seem to lie nearer the periphery, basic 
rocks occupying the central portions. How far thisis true 
can only be ascertained by analyses of a large number of 
rocks, but in the case of the area dealt with in this paper, 
this seems to be true, as its intermediate rocks hold a 
position relatively near the shores of this old lake basin. 
A bulletin’ of the Geological Survey Department recently 
published dealing with the geology of the Cambewarra 
Ranges, is of immense importance as affording most valu- 
able evidence of volcanic activity contemporaneous with 
the sedimentation in the Permo-Carbonaceous coal basin 
already referred to. Here it isshown that flows of trachyte 
and associated tuffs constitute a thickness of about 1,000 
+ Records of Geological Survey of N.S.W., Vol. vit., part i1., 1902, p. 93; 
part ili., 1902, p. 226; part iii., 1903, p. 236. 
? Ibid., pp. 103 - 140. 
