185 
The most easterly dyke is much decomposed, and consists of a fine¬ 
grained, neutral-coloured ground mass, through which is scattered numerous 
felspar crystals, some of a pink colour. This dyke is 6 feet in width. 
The second dyke somewhat resembles the above in colour, but has a 
great abundance of mica. It is quite probable that these two dykes repre¬ 
sent slight differences from the same intrusion, and are probably referable 
to the lamprophyres or allied alkali rocks. 
The third or most westerly dyke attains a width of 14 feet, and consists 
of a white decomposed matrix, through which scattered felspar crystals 
and more rarely small blebs of quartz occur. This dyke probably belongs 
to the quartz porphyry or felsite series- Scattered acicular rods up to 
T | inch in length probably represent what were originally crystals of 
hornblende. Joints intersect the mass in various directions, and along these 
joints a secondary product, of a greasy appearance, ranging up to an 
eighth of an inch in width occurs. This was identified as chloropal at the 
laboratory. 
For a width of a couple of feet on either side of these dykes the strata 
are indurated, the slates breaking in small rectangular blocks. 
Although from a practical point of view the results so far have not 
been successful, more light is now shown on the nature of the gold occur¬ 
rence. It appears probable that the rich specimens and the rich alluvial 
obtained from the outcrop came from flat veins of quartz, of which some 
four or five are now exposed. I was shown a shallow cut where half-an- 
ounce of gold to the dish of dirt was obtained in the past, and this was in 
a belt of purple-coloured slates. This slate was identical in colour and 
appearance with that in which rich yields have been obtained in the shallow 
reef workings at Little Bendigo, near Ballarat. This slate might, there¬ 
fore, be regarded as a favorable bed or indicator. From the shaft work¬ 
ings, &c., it appears that this belt of slate dips east, and, in my opinion, 
auriferous stone is most likely to be found at the intersection of quartz 
veins with this slate. The association of the veins and the dykes is not 
yet apparent, but it is quite likely that the felspar porphyry dyke is earlier 
than the reef, while the mica porphyrite is probably later. This assump¬ 
tion is based on observation of similar dykes—on apparently the same line 
of strike—to the west of Little Bendigo. 
As to suggestions for future workings, it is advisable that the veins 
cut in the shaft be followed west to prove whether the dyke has or has not 
any beneficial effect upon them. 
A cross-cut should be put out easterly from the bottom of the shaft 
for a distance of at least 100 feet. Any veins parallel to those alreadv 
cut would then be intersected. On meeting the belt of nurple slate, which 
probably at this depth would be found to be pvritous, a rise could be.put 
up to prove if any veins passed through in cross-cut were auriferous. 
[.Report sent in 15.11.07.] 
THE AGE OF THE ROCKS AT MARONG AND DUNOLLY. 
By T. S. Hall , M.A., D.Sc., Melbourne University. 
The Age of the Rocks at Marong. 
In reply to the request of the Director of the Geological Survey that 
I should, if possible, fix more definitely the horizon of the rocks at Marong 
which yielded graptolites Nos. 1873-1900, I have the honour to state 
