36 
Geology and Physical Geography : 
It is very likely, however, that the classification of the rocks of 
a considerable area in the eastern part of the colony may have to 
be altered from Lower to Upper Silurian, if further investigation 
tends to corroborate some slight evidence already obtained in that 
direction. 
The ranges consisting of Lower Silurian rocks in the western 
portion of Victoria nowhere greatly exceeded 2,000 feet in altitude, 
and are generally much lower. The axial lino of the Main 
Divide is nearly at right angles to the strike of the rock layers, 
while the courses of the principal rivers and creeks, and of the 
leading spurs separating them, approximately conform to the latter 
in general direction. Portion of the eastern (presumably Lower) 
Silurian area is more alpine in its character ; the two highest 
mountains, Mounts Ilotham aud Feathertop, exceed 6,000 feet in 
height, and the features of the country are on a grander scale than 
in the western area, where the character of the Lower Silurian 
ranges is marked by a general sameness. 
Upper Silurian Rocks. 
As before stated, the provcdly Upper Silurian rocks occupy the 
central portion of the main mountain system of Victoria, within 
an area of about 100 miles in width, bounded on the west by a line 
from Melbourne to Heathcote, and ou the east by the Macalister 
River and a line thence to Benalla. 
The northernmost extension of the rocks of this area is where 
they slope beneath the Murray Tertiaries, at the extremity of the 
Mount Camel Range ; ami their southernmost exposure, separated 
by an area of superimposed Mesozoic rocks from the spurs of the 
Main Divide, but without doubt continuous with the latter under 
the Mesozoic rocks, is within a tract bordering the coast of 
Waratah Ray and Corner Inlet, from Cripe Liptrap to the Bennison 
River, near Foster. About 10 miles north of Foster a small 
outcrop of Upper Silurian rocks through the Mesozoic strata 
occurs at TurtoiFs Creek. , 
Mr. A. R. C. Selwyn remarks, in his work, that “a considerable 
unconformity certainly exists between the Upper aud Lower 
Silurian groups ; they present differences in general lithological 
character and physical structure similar to those observed between 
the same groups in Britain.” 
I conceive, however, that the unconformity here remarked by 
Mr. Selwyn simply refers to their lithological character, as the 
precise lines of junction of the two groups have not been so 
nearly ascertained as to enable it to be stated that they are strati- 
graphically uncouformahle. 
The undulations of the Upper Silurian rocks appear to be less 
frequent than those of the Lower ; the average rate of dip is also 
less in tho former, the general rate being from 15° to 80°, though 
