12 STUDIES, SCIENTIFIC AND SOCIAL chap, i 



So continuous are the bounding lines of cliff, that to descend into 

 some of these valleys it is necessary to go round twenty miles ; and 

 into others the surveyors have only lately penetrated, and the 

 colonists have not yet been able to drive in their cattle. But the 

 most remarkable point of structure of these valleys is that, although 

 several miles wide at their upper parts, they generally contract 

 towards their mouths to such a degree as to become impassable. 

 The Surveyor-General, Sir T. Mitchell, in vain endeavoured, first 

 on foot and .then by crawling between the great fallen fragments 

 of sandstone, to ascend through the gorge by which the river 

 Grose joins the Nepean ; yet the valley of the Grose, in its upper 

 part, as I saw, forms a magnificent basin some miles across, and is 

 on all sides surrounded by cliffs, the summits of which are nowhere 

 less than 3,000 feet above the sea-level. When cattle are driven 

 into the valley of the Wolgan by a path partly cut by the colonists, 

 they cannot escape ; for this valley is in every other part surrounded 

 by perpendicular cliffs, and eight miles lower down it contracts 

 from an average width of half a mile to a mere chasm, impassable 

 to man or beast. ^ 



The view here described by Darwin is that from " Go- 

 vett's Leap " into the Grose Valley, and is shown in the 

 accompanying reproductions from photographs (Figs. 5, 6), 

 but I have not been able to obtain any really good views 

 of the interior of these remarkable cliff-bound valleys. 

 They are also described in Darwin's Naturalist's Voyage, 

 p. 438. 



The origin of these valleys appears to have been as 

 great a puzzle to the early explorers as was that of the 

 Yosemite. Sir Thomas Mitchell estimates that 134 cubic 

 miles of rock must have been removed from the valley of 

 the Grose alone ; and he remarks on the absence of indica- 

 tion of the agency by which these vast masses of stone have 

 been carried away, there being no accumulations of sand, 

 though there are many huge blocks of rock, scarcely worn 

 by attrition, in the bed of the stream, while in the valleys 

 below, instead of sandy deposits, there is a rich alluvium. 

 Even Darwin was staggered at the idea of these enclosed 

 valleys being hollowed out by aqueous erosion. Neither 

 does he accept subsidence, on account of the numerous 

 irregularly branching arms. The resemblance of the clitfs 

 to those of a bold sea coast suggests marine action, " but 



1 The Wolgan is a north-western tributary of the Hawkesbury River, 

 while the Nepean and Grose rivers flow into it from the south-west. 



