BY ALEX. G. HAMILTON. 347 



mentioned are the remnants of a once continuous sheet of volcanic 

 rock which originally probably welled up at' Mt. Wilson and 

 overspread the surrounding area to a now unknown extent (5 

 and 7). Mt. King George is, accoi'ding to the parish map, 5 miles 

 in a straight line from Mt. Wilson, and Tomah and Bell 4 miles; 

 the intervening country is occupied by an intricate network of 

 ravines with the characteristic precipitous sides found in valleys 

 in the Hawkesbury Sandstone region. 



On the eastern side of Mt. Wilson, Waterfall Creek, a tributary 

 of the Bowen, takes its rise and falls over the edge of the basaltic 

 sheet, which there is 275 feet below the summit and about 100 

 yards wide. Here there is basalt of a massive character, while 

 50 or 60 yards up the creek it splits into thin flat pieces, which 

 ring like a piece of metal. The rock is also found in roughly 

 prismatic columns in places. It usually weathers irregularly all 

 over, the large crystals decomposing first and leaving hollows like 

 gas bubbles. But in one spot boulders embedded in the soil 

 decompose concentrically, so that the weathered stujff comes off in 

 layers like the coats of an onion. The product of the weathering 

 is a soil usually red, but sometimes approaching a chocolate 

 colour. 



Here and there zeolites are found throughout the mass. Mr. 

 George Card, A.R.8.M., has been good enough to examine a 

 micro-section of the rock, and gives me the following description 

 of it: — "The rock is an olivine basalt. The minerals present 

 are olivine, augite, plagioclase felspar (probably Labradorite), 

 magnetic (and other) iron oxides. These are embedded in a 

 light brown glass. The felspar microlites give rise by their 

 disposition to a good fluidal structure, floating round the por- 

 phyritic constituent. 01i^'ine is abundant and remarkably fresh. 

 It occurs as porphyritic individuals, presumably fi-om an earlier 

 stage of crystallization, and numerous granules through the rock. 

 The augite has a tendency to assume a purplish tint, and is 

 slightly pleochroic." The basalt of Mt. Irvine is of a similar 

 character. 



