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Letter 468

Darwin, C. R. to Mitchell, T. L.

[Feb 1839 – Aug 1842]

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    Sends suggestions for points that would interest geologists in a description of valleys in the Blue Mountains [New South Wales].

Transcription

My dear Sir

The chief object in the description of the valleys, which would interest geologists, I should think would lie in as clear an indication as possible of the amount of solid stone removed in these excavations—

To show this of course would require only measurements of the depth, breadth, & length.— You might describe the bounding lines of some one valley, & state (if you have knowledge of the fact) that a line of cliffs, such as those given in your drawing, stretch continuously for so many miles, inclosing such an area, & having a height nearly equal or lowering towards some point of the compass, or whatever the facts might turn out.— The second class of facts to mention; is the direction through which the great area of stone has been removed.—

this will require a description of the lower part of those valleys, of which the upper forms one of the basins.— the width & depth of the gorge; its impassibility &c.—the present size & force of the stream &c &c.—

I suspect, no one at present could do more than state the problem. its solution appears to me most difficult. Of course you must allude to the nature of the sandstone on the Blue Mountains, its horizontal stratification &c; & the consequence that these valleys are due to excavation, & not to the elevation of a line of hills on each side as might be supposed.

These are the few suggestions which occur to me.—

very Faithfully yours | Chas. Darwin

    Footnotes Add

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    f1 468.f1
    Mitchell came to London in July 1837 on leave from his post as Surveyor-general in New South Wales. During his stay he published an account of his exploration in Australia (Mitchell 1838).
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    f2 468.f2
    For Mitchell's description of the valleys, and particularly of Wellington Valley, see Mitchell 1838, vol. 2, ch. 15. CD had visited the Blue Mountains, west of Sydney, in January 1836 (see DAR 38.1: 829–36 for his field notes, summarised in Journal and remarks, pp. 522–4). In Volcanic islands, pp. 134–7, the description of the valleys is considerably expanded. CD thanks Mitchell for ‘several interesting personal communications’ on the subject.
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