416 The Rev. S. Haughton on Slaty CleavagCj 



itself in a very deep sea, so ingeniously imagined lately by Mr. 

 Babbage. Whatever may have been the primary conditions 

 under which this compression took place, it is certainly interest- 

 ing to have an exact numerical measure of its amount. 



Example 4,-^Lingida Beds of the Loiver Silurian epoch, 

 Abereiddy Bay, Pembrokeshire, 

 These beds consist of a soft, black, carbonaceous shale, and 

 present the appearance of having been considerably compressed. 

 There is no distortion of fossils in the cleavage plane itself, a fact 

 that falls in with what I have before noted of the shales of Water- 

 ford and South Petherwin. The fossils on which I have made 

 my calculations are Lingula Phillipsii (Salter)* and Calymene 

 duplicata. The normal shapes of these fossils are here given : — 



Lingula Phillipsii . Length =184 

 Breadth = 173 



Calymene duplicata . Length of body . . . =121 

 Length of tail . . . . = 64 

 Maximum breadth of body =143 

 Breadth ofbody two-thirds 1 __-|Q-f 



down from the thorax. / ~ 

 Breadth of tail ... =108 



The following data were obtained by the measurement of the 

 distorted specimens of these fossils :■ — 



</)=0, -=1 Lingula Phillipsii 



r 



</>'=13°, -, = 1-950 Lingula Phillipsii 



1*893 Lingula Phillipsii 



1 1*846 Lingula Phillipsii 



1*725 Calymene duplicata 



1*732 Calymene duplicata 



Mean . . 1*829 

 From these data w^e obtain, as before, — 

 1 



= 1 



a 



I- 



-=6*881 

 c 



(D) 



* I would here express, once for all, the great obligations I have been 

 under to Mr. J. W. Salter of the Geological Survey, Jermyn Street. His 



