ANNIVERSARY ADDRESS. 61 
time. The evidence is tolerably clear as to their having intruded 
the Hawkesbury Sandstone as well as the coal-measures, and 
as to there having been a powerful upward flow of» paroxysmal 
violence. At first sight, therefore, one would infer that they 
mark the site of old volcanic chimneys. This was probably their 
- function, though the slightly altered condition of the fragments of 
bituminous coal seems incompatible with an intimate association 
with a matrix of voleanic rock. The highly brecciated character 
of the mass, however, shews that superheated water producing 
violent steam explosions was probably abundantly present, and 
this may have protected the coal from calcination such as it has 
undergone when in contact with the basic dykes at Cremorne. 
There is here, therefore, a fine field for further investigation. 
About twenty miles east of the Valley is a large eruptive mass 
of very coarse dolerite at Prospect Hill (Waimalee). The Rev. 
W. B. Clarke,! has referred to this mass :—‘“ At Waimalee on 
Prospect Hill, west of Parramatta, the magnetic diorite which 
‘there occurs, and which is, probably, the summit of a concealed 
mass submerged during the Carboniferous period and belonging 
to the Auriferous Epoch, has furnished the material of fern bear- 
ing beds of this division, that rest upon the diorite, and have 
since been intruded into and altered by basalt, which, in another 
part of the hill, exhibits a columnar structure.” This so-called 
“magnetic diorite” is now known to be a crystalline-granular 
dolerite rich in titaniferous iron and analecime, Drusy cavities, 
one to four feet in diameter, are occasionally met with, having 
their sides lined with prehnite. The dolerite graduates into the 
basalt, and there is clear evidence that both have intruded the 
overlying Wianamatta Shales, which in places are converted into 
chert at the point of contact. No trace of any breccia has yet 
been noticed. Probably this mass which is over half a mile in 
diameter represents the material which has consolidated in the 
reservoir of a now deeply denuded volcano. About ten miles 
1 Researches in the Southern Goldfields of N.S. Wales, Second Edition 
Sydney, 1860, p. 248. 
