199 
At the points marked by crosses, boulders of cemented river-wash are 
to be obtained in the surface soil at the contact of the basalt, and are 
evidently the remains of an old water channel, which has been filled by 
the basaltic flow. 
I also crossed over a portion of the Dandenong dacites, between Olinda 
Vale and Monbulk settlement, and endeavoured to find any traces of the 
occurrence of any Silurian inkers, but as I was unsuccessful, and could not 
hear of any indications from residents familiar with the locality, I do 
not think there are any in this portion of the mass. 
[Report sent in i^..8.oj.\ 
BOUNDARIES OF FORMATIONS BETWEEN THE HEAD OF 
THE ACHERON AND YEA RIVERS AND THE YARRA. 
By J. Easton . 
The following observations were made during a rapid delineation of the 
geological boundaries! of the area of igneous rocks occuring between the 
head waters of the Acheron and Yea Rivers on the north, and the Yarra 
River on the south. 
This area is situated in portions of the counties of Evelyn and Anglesey, 
and includes several prominent mountain peaks such as St. Leonard, 
Monda, and Strickland, on the main divide, and, south of the divide, 
Mounts Juliet and Donna Buang. The last-named is 4,080 feet in height, 
and is the highest point within the area. 
The boundaries of the formations, so far as I was able to determine 
them, are shown on the accompanying sketch plan. 
These boundaries, in many places, are only approximate, as I was 
unable, in the limited time at my disposal, to traverse the whole of 
them. Portions of this area are covered with such a dense undergrowth 
that in places it is almost impenetrable. 
The formation which is termed trap on the Geological Map of Vic¬ 
toria, and referred to and described in sundry reports as plutonic and allied 
to the granites, has recently been shown to be a dacite by Prof. J. W H 
Gregory, D.Sc., E.R.S., in his paper on the geology of Mt. Macedon. 
Phis mountain he considers to be an allied mass, probably the remains of a 
Mesozoic or early Cainozoic volcano. 
In lithological characters these rocks vary from finely crystalline dacite 
in such places as the Blacks’ Spur, Warburton, Ligar River, &c., to more 
coarse-grained biotite-dacite at Mounts Juliet, Strickland, and the Rock. 
At Mt. St. Leonard it is more porphvritic, and is made up of fairlv 
large crystals of Quartz and felspar in a. dense ground mass. . Near the 
Yarra River, about i| miles above Warburton, - and to the west of the 
Dee River (see 2 a and 4A on the sketch map), I obtained samples of 
trachy-phonolite, but it would be impossible to define its extent without a 
more detailed examination . 
Tuffs also occur at several points (see locality plan), and generallv 
rest on the Silurian rocks near the edge of the dacite. The best section of 
these tuffs is shown on the Don road, between Healesville and Launching- 
Place, on the south side of the Coranderrk or Badger Creek, where they 
can be seen for a distance of half-a-mile along the road cutting, and 
re-sting on the Silurian strata which are dipping under them at an angle of 
about 65 deg. in an easterly direction, and do not appear to be in anv 
way affected by the close. proximity of the tuffs and dacites. The tuffs 
