ORIGIN OF VALLEYS. B74 
gulfs, with walled sides, composed of horizontal layers of sandstone. 
These layers seem once to have been continuous; and what is the 
force which has thus channelled the mountain structure? Are they 
“stupendous rents in the bosom of the earth ?”* Are they regions of 
subsidence? Can it be that they were never filled, but were depres- 
sions left between the heaps of accumulating sediment that constitute 
the sandstone, which depressions were afterwards enlarged by the sea 
during the elevations of the land?+ Or may we adopt the “ prepos- 
terous” idea, that sirnple running water has been the agent; and if so, 
was it fresh water, or the ocean? 
The forms of these valleys are as remarkable as their extent. Major 
Mitchell states that Cox’s River rises in the Vale of Clywd, 2150 feet 
above the sea, and leaves this expanded basin through a gorge 2200 
yards wide, flanked on each side by rocks of horizontally stratified 
sandstone eight hundred feet high: here it joins the Warragamba. 
Some of its tributaries rise at a height of 3500 feet above the sea, and 
the ravines they occupy cover an area of 1212 square miles. From 
this he calculates that one hundred and thirty-four cubic miles of stone 
have been removed from the valley of the Cox.{ ‘The facts observed 
by us are sufficient to substantiate the general result, although we 
cannot add definite estimates of our own. The Kangaroo Valley is 
another example of a valley, two to three miles in width, and a thou- 
sand feet to eighteen hundred deep, opening outward through a com- 
paratively narrow gap: and by a rough calculation from our own 
examinations, and the map of Major Mitchell, the amount of rock 
necessary to fill the valley is equivalent to a rectangular ridge, twelve 
miles long, two miles wide, and two thousand feet high. On the map 
of the Illawarra District, the form of this valley, (from the colonial sur- 
veys,) may be seen; and it is interesting as an illustration of the 
general character of these sandstone gorges, though wider than many 
of them in proportion to its length. This is but a small example, how- 
ever, compared with those of the interior. Mr. Darwin remarks upon 
this peculiarity of form,—their extent and width and many branches, 
yet narrow openings at their lower extremity ;2and he observes that 
the same is the character of the bays along the coast. 
In studying the origin of these valleys, we have then to consider 
the following particulars :— 
* Strzelecki’s New South Wales and Van Diemen’s Land, p. 57. 
t Darwin’s Volcanic Islands, p. 137. 
+ Expedition into Australia, ii, 352. 
