24 
Geology and Physical Geography : 
So far as this tract has been superficially examined, no arbitrary 
line of demarcation between the granite and the trap can be laid 
down. The general characters displayed by the latter are various, 
but of some typical samples I am fortunately able to quote the 
following descriptions, supplied by Mr. A. W. Howitt, F.G.S., 
who has made the microscopical investigation of rock-structure 
one of his special studies, and who has kindly examined for me a 
largo number of igneous rock-specimens : — 
“ MASSIVE TRAr, NEAR HEALESV1LLE, 
“ Ground-mass, micro-crystalline, consisting of felspar and 
quartz. In it are— (1) Crystals of quartz; (2) Orthoclase crystals. 
No triclinic felspar observable, but a little mica (? muscovite), 
which is quite subordinate. In composition, this is a quartz- 
felsite.” 
Another specimen of trap rock from the Watts River, near 
Healesville “ This is a quartz porphyrite (hornblendicy* 
No. 1 specimen, from north of Yarra River, opposito Warburton. 
— “Ground-mass, micro- crystalline, of quartz and felspar and a 
little magnetite. In it arc— (1) Felspar, mostly plagioclase ; (2) 
Chlorite pseudomorphs after hornblende ; (3) Masses of felsitic 
ground-mass. This is a hornblende porphyrite.” 
No. 2, north of Yarra River, opposite Warburton. — “ This rock 
is in character between a quartz porphyrite and a quartz felsite, 
there being both orthoclase and plagioclase felspars.” 
Two remarkable belts, resembling enormous dykes, are indicated 
as trappean on the Geological Sketch-map. One forms the summit 
of the Mount Stnveley Range, south from the Grampians, between 
Wickl iff e a n d Dunk el d, an d protrudes through Lower Silurian rocks. 
Judging from a hand-specimen, the rock is a felspar porphyry, 
but I have not had an opportunity of obtaining information irom 
personal observation as to the extent and character of the outcrop. 
The second forms the ridge of the Mount Camel Range, 10 
miles north from Iluatlicote, and the rock consists there of a dark, 
dense, hornblendic greenstone diorite — hornblende rock. It is in 
the same line of strike with a large dyke of fine granite which 
passes through Heatbcote. 
Still further to the south, in the same direction, another long 
outcrop of greenstoue diorite forms a range to the east of Lance- 
field. The entire belt, from Mount Camel to Lancefield, follows 
approximately the apparent boundary line between the Lower and 
Upper Silurian rocks. 
Jlr. Norman Taylor describes the rock near Lancefield as being 
very variable in its mineralogical character, some varieties being 
greenish-black and dense (aphanitic), others light-green and por- 
phyritic, and others nearly black, crystalline, and very hornblendic. 
