LETTER 536. TO D. SHARPE.

(536/1. The following eight letters were written at a time when the
subjects of cleavage and foliation were already occupying the minds of
several geologists, including Sharpe, Sorby, Rogers, Haughton, Phillips,
and Tyndall. The paper by Sharpe referred to was published in 1847
("Quart. Journ. Geol. Soc." Volume III.), and his ideas were amplified in
two later papers (ibid., Volume V., 1849, and "Phil. Trans." 1852).
Darwin's own views, based on his observations during the "Beagle"
expedition, had appeared in Chapter XIII. of "South America" (1846) and in
the "Manual of Scientific Enquiry" (1849), but are perhaps nowhere so
clearly expressed as in this correspondence. His most important
contribution to the question was in establishing the fact that foliation is
often a part of the same process as cleavage, and is in nowise necessarily
connected with planes of stratification. Herein he was opposed to Lyell
and the other geologists of the day, but time has made good his position.
The postscript to Letter 542 is especially interesting. We are indebted to
Mr. Harker, of St. John's College, for this note.)

Down, August 23rd [1846?].

I must just send one line to thank you for your note, and to say how
heartily glad I am that you stick to the cleavage and foliation question.
Nothing will ever convince me that it is not a noble subject of
investigation, which will lead some day to great views. I think it quite
extraordinary how little the subject seems to interest British geologists.
You will, I think live to see the importance of your paper recognised.
(536/2. Probably the paper "On Slaty Cleavage." "Quart. Journ. Geol.
Soc." Volume III., page 74, 1847.) I had always thought that Studer was