186 THE GEOLOGY OF DUBBO, 



The outcrop of the coal on Spicer's Creek is near the edge of the 

 coal " basin." A series of borings from this point following the 

 dip of the beds would be the most eflective method of proving that 

 portion of the country. 



Fireclay. — Thick beds of fireclay underlie the coal and ironstones 

 at Ballimore. It is true that some specimens, sent to experts, were 

 considered hardly suitable for the manufacture of fire-bricks. But 

 it has been remarked that though chemical and minei^alogical 

 examination will often enable us to say that certain clays will 

 assuredly not make fire-bi-icks ; and that other clays are promising 

 enough to make it worth while trying them ; yet nothing short of 

 making a test brick will settle the question. No bricks have been 

 made as yet. 



Freestone. — The sandstone is quarried in a few places for building 

 stone. The best procurable is more friable and less ferruginous 

 than Pyrmont stone, nor will it bear an equal weight. In fact 

 the normal sandstone is hardly more than a mixtui-e of quartz 

 grains, decomposed felspar and mica, without any chemical union. 

 In the proximity of basalt it is altered and more compact, and 

 often changed into a quartzite, as at Barbigal and Dalton's 

 Paddock, near the general cemetery. From some experiments I 

 made with the building stone, I found that blocks of a cubic inch 

 placed in water to a fourth of their depth, absorbed more than one- 

 half of their own volume of water. Cubes repeatedly saturated 

 with a solution of common salt lose their angles, and when treated 

 in the same way with sulphate of soda rapidly disintegrate. The 

 altered sandstones already referred to as quartzite, make a building 

 stone durable as granite. 



Granite. — It is v/ell exposed on the the railway at 289-10 miles. 

 It is a ternary granite, hornblende replacing the mica to a great 

 extent. It takes a fine polish, having a slightly bluish tinge. 

 Nothing shows how compact the crystals are better than the quality 

 it possesses of holding together when reduced to thin slices for 

 microscopic examination. In the near future it will be used for 

 building purposes, as it is unquestionably the most durable stone 



