THE 

 LONDON, EDINBURGH a.nd DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND ' 



JOURNAL OF SCIENCE. 



» 



[FOURTH SERIES.] 



DECEMBER 1856. 



LII. On Slaty Cleavage, and the Distortion of Fossils, By the 

 Rev. Samuel Haughton, Professor of Geology in the Uni- 

 versity of Dublin^. 

 THE first person, so far as I know, who distinctly put for- 

 ward a purely mechanical theory of slaty cleavage, was the 

 late Mr. Sharpe, in two papers read before the Geological Society 

 of London, December 2, 1846, and November 1, 1848. These 

 papers are published in the third and fifth volumes of the Quar- 

 terly Journal of that Society, and form a most valuable basis of 

 well-observed facts on which to establish a mechanical theory of 

 slaty cleavage. At the close of the second of these papers, Mr. 

 Sharpe sums up his observations as follows : — 



"Thus all our observations and deductions ultimately con- 

 verge to the conclusion, that the cleavage must be attributed to 

 pressure caused by the elevation of great masses of rock under 

 conditions of which we are ignorant. And if to this conclusion 

 it should be objected that no similar results can be produced by 

 experiment, I reply that we have never tried the experiment with 

 a power at all to be compared with that employed ; and that this 

 may be one of many cases where our attempts to imitate the 

 operations of nature fail, owing to the feebleness of our means, 

 and the shortness of the perigd during which we can employ 

 them.'' 



The objection thus alluded to by Mr. Sharpe has been com- 

 pletely removed by the illustrative experiments of Professor 

 Tyndall, who deserves the thanks of geologists for the light he 

 has thrown upon this obscure question. In common, I believe, 



* Communicated by the Author. 

 Phil Mag, S. 4. Vol. 12. No. 81 . Dec. 1856. 2 E 



