1846- 1856] CLEAVAGE AND FOLIATION 



V. Cleavage and Foliation, [846-56. Letter 536 



To D. Sharj 



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 Sharpc, Sorby, Rogers, Haughton, Phillips, and 

 Tyndall. The paper by Sharpe referred to was published in 1847 (Quart. 

 Journ. Geol. Soc, Vol. III.), and his ideas were amplified in two later 

 papers {ibid., Vol. V., [849, and Phil. Trans., 1852). Darwin's own 

 views, based on his observations during the expedition, had 



appeared in Chap. 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 sanu- 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 arc indebted to 

 Mr. Marker, of St. John's College, for this note. 



Down, Aug. 23rd [1846?]. 



I must just send one line to thank you fur your note, and 

 to say how heartily glad 1 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, 1 think, live to see the importance of your 



asleader. Another expedition left Sydney in 1897 under the direction of 

 Prof. Edgeworth David, anil a deeper boring was made. The Reports 

 will be published in the Philosophical Transactions, and will contain Prof. 

 David's notes upon the boring and the island generally, Dr. Hindi 

 description of the microscopic structure of the cores and other examina- 

 tions of them, carried on at the Royal College of Science, South 

 Kensington. The boring reached a depth of 11 14 ft. ; the cores were 

 found to consist entirely of reef-forming corals in situ and in fragments, 

 with foraminifera and calcareous algae ; at the bottom there were no 

 traces of any other kind of rock. It seems, therefore, to us, that unless 

 it can be proved that reef- building corals began their work at depths of 

 at least 180 fathoms — far below that hitherto assigned — the result gives 

 the strongest support to Darwin's theory of subsidence ; the test which 

 Darwin wished to be applied has been fairly tried, and the verdict is 

 entirely in his favour. 



1 Daniel Sharpc. See not. 3, p. 131. 



