328 FRAGMENTS OF SCIENCE 



facts. This has been done, and the labors of Daniel 

 Sharpe (the late President of the Geological Society, who, 

 to the loss of science and the sorrow of all who knew 

 him, has so suddenly been taken away from ns), Mr. 

 Henry Clifton Sorby, and others, have furnished us with 

 a body of facts associated with slaty cleavage, and having 

 a most important bearing upon the question. 



Fossil shells are found in these slate-rocks. I have 

 here several specimens of such shells in the actual rock, 

 and occupying various positions in regard to the cleavage 

 planes. They are squeezed, distorted, and crushed; in all 

 cases the distortion leads to the inference that the rock 

 which contains these shells has been subjected to enor- 

 mous pressure in a direction at right angles to the planes 

 of cleavage. The shells are all flattened and spread out 

 in these planes. Compare this fossil trilobite of normal 

 proportions with these others which have suffered dis- 

 tortion. Some have lain across, some along, and some 

 oblique to the cleavage of the slate in which they are 

 found; but in all cases the distortion is such as required 

 for its production a compressing force acting at right 

 angles to the planes of cleavage. As the trilobites lay 

 in the mud, the jaws of a gigantic vice appear to have 

 closed upon them and squeezed them into the shapes 

 you see. 



We sometimes find a thin layer of coarse gritty ma- 

 terial, between two layers of finer rock, through which 

 and across the gritty layer pass the planes of lamination. 

 The coarse layer is found bent by the pressure into sinu- 

 osities like a contorted ribbon. Mr. Sorby has described 

 a striking case of this kind. This crumpling can be ex- 

 perimentally imitated; the amount of compression might, 



