BASALTS OF BATHURST AND NEIGHBOURING DISTRIOTS. 299 
mass of basalt is of considerable extent, about three miles in 
length by about a quarter to a third of a mile in breadth, having 
a general north and south trend, with a bend to the west at the 
northern extremity and a smaller one in the same direction at 
the southern end. It forms a connected whole, except for a small 
interruption where the road from Perth to Evan’s Plains crosses 
the hills, and there are two small pinnacle hills with a thin cap 
of loose boulders of basalt, in the direction of Mount Apsley. 
The base of the basalt undulates gently round the hills, but is on 
the whole tolerably level, although it is difficult to determine the 
exact junction with the drift which underlies it, owing to loose 
earth and boulders having rolled or been washed down the sides. 
At the nearest point to the city, the base of the basalt is about 
four hundred and fifty feet above the Bathurst Court House, 
which has been taken as a datum level. The Court House is 
just about fifty feet above the Bathurst Railway Station, which is 
two thousand one hundred and fifty-two feet above sea level, so 
that the datum is, roughly, two thousand two hundred feet above 
the sea. 
The highest part of the Bald Hills is from six hundred and fifty 
to seven hundred feet above the datum, making the thickness of 
the basalt at least two hundred feet over much of the hills. The 
upper part is more or less weathered into large blocks and irregular 
columns, with earthy matter between, and the basalt was once 
probably considerably thicker than it is now. The lower part is 
columnar wherever it can be seen, but is only visible in quarries 
as a rule. There are fortunately, however, quite a number of 
small quarries around the side of the hills between Perth and 
Bathurst. By far the most extensive exposure is that at the 
quarry opened by the Corporation of Bathurst in order to obtain 
“blue metal” for the streets. This has only been opened a few 
years, but already there is a fine face about fifty feet in height. 
The upper part of the face is columnar, but the columns are much 
weathered and broken, only about sixteen feet at the bottom 
shewing tolerably perfect specimens. The floor of the quarry is 
