GEOLOGICAL SOCIETT OF DUBLIN. 99 



What I call the Distortion of a fossil is the quantity — 



m N 

 P = n X M' <!) 



In this expression the fraction m : n represents the ratio of the hori- 

 zontal and vertical measurements of the figures as actually observed in 

 their distorted condition ; and the fraction M;N represents the ratio of 

 the same lines when the fossil is in its natural or undisturbed form. 



In Plate VI. the Figures 1, 1a, 1b, lc, represent fossils distorted by 



Fig. 1 is Orthis crenistria from the Carboniferous Slate of Ardo- 

 ginna, Co. Waterford, with its hinge-line perpendicular to the in- 

 tersection of cleavage and bedding. 

 Fig. 1a represents the same fossil from the Carboniferous Slate of 

 Carrigaline, Co. Cork, with its hinge-line drawn out in the line of 

 intersection of cleavage and bedding. 

 Fig. 1b is a fossil from the same locality as the last, viz., Carriga- 

 line ; but so changed by cleavage, both in and perpendicular to 

 the plane of bedding, as to be hardly recognisable. I name it, 

 with considerable hesitation, Productus caperatus. 

 Fig. lc is a beautiful specimen of Euomphalus pentangulatus, distorted 

 by cleavage, from Little Island, Co. Cork, where these distorted 

 fossils occur in great abundance in limestone, and have been fre- 

 quently, from their form, described asEllipsolithes, and considered 

 as quite distinct from Euomphalus. 

 In the Figs. 2, 2a, 2b, 2c, the artist has reduced the distortion in the 

 proportion of 5:4. In Plate VII., Figs. 3, 3a, 3b, 3c, the distortion is 

 reduced in the proportion of 5 : 3 ; and it is evident to geologists ac- 

 quainted with these fossils that this reduction of their distortion has 

 nearly restored them to their natural shape. In Figs. 4, 4a, 4b, 4c, the 

 reduction of the distortion is continued in the proportion of 5 : 2 ; and it 

 is very instructive to observe that it has now become a distortion in the 

 perpendicular direction, causing Figs. 1 and 1a to change characters in 

 becoming 4 and 4a. 



It is to be remembered that such specimens as 4, 4a, 4c, could not 

 occur in practice, with the intersection of the planes of cleavage and 

 bedding in the horizontal line. In fact, in the figs. 1 and 2, the line of 

 intersection of planes of cleavage and bedding is horizontal ; in Fig. 3 

 there is either no cleavage, or its plane coincides, or nearly coincides, 

 with that of bedding ; and in Fig. 4, the line of intersection of planes of 

 cleavage and bedding must have become at right angles to its former po- 

 sition, and be supposed vertical 



Since publishing the paper alluded to above, I have read with care 

 the various papers published on the subject of cleavage by Mr. Sorby, 

 and feel most happy to bear my testimony to their great value. His 

 methods of research are quite different from my own ; and I am glad to 

 learn that the few results I have obtained independently, from the con- 



