BY THE REV. J. MILNE CURRAN. 179 



An aureole of altered rocks separates the granite from the Silurian 

 slates, phyllites or limestones. In short, we have a great saucer- 

 like depression, the edges of which are silurian rocks ; below these 

 there is a belt of hornfels, or metamorphic rocks, and, finally, 

 granite with recent superficial deposits fills the floor of the valley. 



Through this valley, as stated already, rising abruptly from the 

 general level, there ruDS a line of basalt, burying an old river-bed 

 of pliocene age. The granite, from its first appearance to the east, 

 to the boundary of the silurian rocks on the Bathurst-Orange Road, 

 measures some thirty miles across. From the contact rocks on 

 the Winburnclale Creek, to the junction of the slate and granite, 

 south of Batburst, the distance is some eighteen miles, that is 540 

 square miles. But, allowing for a very irregular line of junction 

 and the small patches of basalt, I take the granite area to measure, 

 at a very moderate estimate, about 460 square miles. 



In this area the lowest rocks — granites and hornfels — are the 

 more recent, as will be made clear in another section of this paper. 



Surface Geology. 



This granite country presents a surface of gently undulating hills 

 and ridges with broad valleys. Except in cuttings in creeks, or on 

 the river-banks, the granite hardly ever shows on the surface, and 

 when it does it is so decomposed as to disintegrate readily and 

 rapidly. As is usual with granite, the decay commences in the 

 felspar grains, thus setting free the other constituents — quartz, 

 hornblende, and biotite. The depth to which decomposition extends 

 varies much ; sometimes to a few feet, and sometimes, in cases 

 that came under my notice, to a depth of 70 feet. The " rolling 

 downs " character of the granite country contrasts strongly with 

 the surface appearances of the surrounding slate. The hills in the 

 slate country show the bed rock freely in escarpments and bars 

 parallel to the strike. The vegetation, moreover, assumes a 

 noticeable change on passing from the granite to the slate country. 

 The accompanying photographs show in an admirable way the 

 difference in weathering in granite and in slate country. Fig. 1 



