ri Building Materials. 25 
mount, but is so connected with our wants and necessities, of 
a common kind, that we cannot but injuriously sacrifice it to 
consideration of cost, time, and convenience. . 
As this paper will treat more particularly of the building 
materials used in Melbourne, it is necessary to remark that 
the geological character of the district is similar to that from 
whence are derived some of the best building stone in 
Great Britain. The prevailing formation is inclined sand- 
stone and clay slate, changing so much in its lithological 
character that, had we not clear and satisfactory evidence of 
its antiquity, it might sometimes be mistaken for a recent 
‘ deposit. We find it in every variety of sandstone, from a 
coarse grit to that of a fine, close-grained structure, which 
last passes into a claystone, containing very few quartz grains, 
and a little white mica. 
Overlying this, and extending through a considerable 
area, is the Basalt, or “ Bluestone,” which is well adapted 
to structural purposes, and generally obtains where durability 
is desired. The rock is recognised by geologists as a vol- 
canic product, and may be considered second only to the 
Plutonic rocks, in its wide distribution and economic im- 
portance. 
BASALT. 
The specimens that I have examined differ very little in 
their composition as far as it effects their durability ; though 
the proportions of their chemical constituents are variable. 
- It is composed of angite, felspar, iron, and lime, with occa- 
sional crystals of olivine; and the contact of these minerals 
is close and perfect. The most common colour is greyish 
blue. ‘The fracture is uneven. An analysis shows its com- 
ponent parts to be—* 
Silex te by hs 50 
Alumina Pe is ae 22 
Carbonate of Lime ah 10 
Magnesia... at a 4 
Tron .. a ah ei 10 
Loss .. nh bs ie 4 
It sometimes contains traces of other metals, but this analysis 
gives its most important constituents. The average weight 
of a cubic foot is 165 lbs., the maxium being 167 lbs., and 
* The figures in this analysis must be considered only as approximate; my 
appliances not being of a kind to ensure rigid accuracy. 
