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 

 considerations of cost, time, and convenience. 



As this paper Mill 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 stones 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 in it 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. This 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 shews its com- 

 ponent parts to be — * 



Silex 



Alumina ... 

 Carbonate of Lime 

 Magnesia ... 

 Iron 

 Loss 



50 

 22 

 10 



4 

 10 



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 maximum being 167 lbs., and 



* The figures in this analysis must he considered only as approximate ; my 

 appliances not being of a kind to ensure rigid accuracy. 



