In the eastern part of Australia the geologist will certainly find sections in abundance but they are nearly all of sandstone for, with few exceptions no other rocks have been denuded in situations similarly exposed.

GEOLOGICAL STRUCTURE AND PHYSICAL OUTLINE.  VALLEYS OF EXCAVATION.  EXTENT OF THAT OF THE COX.

The ravines which discharge their waters into the little river Cox occupy an area of 1,212 square miles, or one-half of the county of Westmoreland on the right or south side of that river, and one-fourth of the county of Cook on the other.  Of this area 796 square miles, equal to one-half of the county of Westmoreland, are on the right or south side of that river, and 416, or one-fourth of the county of Cook, on the left.  The whole extent comprises the basin of this mountain stream, and is bounded by heights rising very gradually from about 1000 feet at the gorge or outlet of the Cox, to 3,400 feet on the north side at Blackheath, and on the south to Murruin and Werong, summits of still greater elevation; the lowest part of the ridge bounding this basin on the west or interior side being nearly 3000 feet above the level of the sea.  Cox’s river flows over a bed of water-worn rocks which, in the upper part of the valley, is 2,150 feet above the sea, and on the road to Bathurst this bed consists of trap and granite.  The river falls rapidly on leaving the granite of the vale of Clwyd to a level not much above that of the sea, and it escapes near its junction with the Warragamba from this spacious basin through a gorge about 2,200 yards wide and flanked on each side by points about 800 feet high.

QUANTITY OF ROCK REMOVED.

Supposing but two-thirds of the enclosed area of sandstone to have been excavated to the depth of 880 feet only, which I allow as the mean thickness of the stratum thus broken into, and considering the inclination of the Cox and other valleys, then 134 CUBIC MILES of stone must have been removed from this basin of the Cox alone.

VALLEY OF THE GROSE.

The valley of the Grose, whose basin is contiguous to that of the Cox on the north, is of less extent but enclosed by cliffs of greater perpendicular height.  That river has been already described in the journal, and the general character of the valley through which it flows is represented in Plate 10 Volume 1.* We now perceive but slight indications of the action by which the great area of stone in the valley of the Cox, the Grose etc. has been removed.  There are no accumulations of sand but huge blocks of rock, scarcely worn by attrition, occur in great abundance in the bed of the stream; neither do we find in the larger channels of the rivers below any sand deposits, but on the contrary the very rich alluvium which distinguishes the banks of the Hawkesbury.

(Footnote.  This book is already almost too full of plates and I beg to refer the geological reader to my three-sheet map of the Colony for the superficial forms and extent of these valleys.)