76 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 2, 



a trace of cleavage, there was evidently some connection between the 

 direction in which the specimens had been altered and the direction 

 of the cleavage. But that connection appeared so complicated that 

 I saw no prospect of understanding it without visiting some localities 

 where the phsenomena might be examined on the spot on a large 

 scale. Besides certain agreements in the direction of the cleavage 

 and the distortion, it appeared to be nearly a general rule that the 

 shells are most distorted in those beds which are most slaty ; which 

 confirmed the idea that the two phsenomena were intimately connected. 



The only remarks I could find on the subject are contained in a 

 short paper by Professor Phillips, read to the British Association in 

 184'3, 'On certain Movements in the Parts of Stratified Rocks,' from 

 which the following is an extract : — " The layers of shells in slaty 

 rocks were generally distinctly marked by ferruginous lines, caused 

 by their decomposition, and the form of their outlines was often re- 

 markably changed. The Leptsense in North Devon assumed the 

 formof Nuculae, and theSpirifers were crumpled up, or else extremely 

 attenuated. The Trilobites of the Llandeilo flags were found in 

 three distinct forms, arising from the distortion taking place in a 

 longitudinal, transverse, or oblique direction ; this seemed to be the 

 result of a creeping movement of the particles of the rock along the 

 planes of cleavage, the effect of which was to roll them forward, in a 

 direction always uniform, over the same tract of country : the move- 

 ment does not seem to have affected the hard shells, but only those 

 which were thin, as also the Algse and Trilobites: the latter are 

 covered with little folds, parallel to the wave of motion. In these 

 distorted fossils the amount of movement might be estimated ; as, in 

 the space occupied by a Trilobite, it amounts to a quarter or even 

 half an inch*," &c. It i? evident from this extract, that Mr. Phillips 

 had already discovered a connection between the distortion of the 

 fossils and the cleavage of the rocks containing them ; but I am not 

 aware that he has followed up the subject. 



I had no hesitation in selecting Tintagel and South Petherwin as 

 the most favourable spots to visit for the accomplishment of the ob- 

 ject in view; the former locality especially so, as it affords large 

 specimens of Spirifers most extravagantly distorted f. The size of 

 the specimens facilitates comparison and measurement, and it is 

 obviously desirable to hiMve to do with shells originally equilateral ; 

 for though distortion may be visible in such shells as Aviculae, Pteri- 

 nese and Posidonise, their forms are essentially so irregular that we can 

 form no calculation of its amount. Our colleague Mr. S. R. Pattison, 

 who collected the Tintagel specimens figured in the Geological 

 Transactions, was kind enough to accompany me to Tintagel, and to 

 assist me in my researches both there and in his own neighbourhood 

 of Launceston, 



Tintagel stands upon the upper part of the beds of the Devonian 

 system : to the south of the village some large slate quarries have 

 been worked on the face of the cliff, but they are now abandoned. 



^ Report of the Meeting of the British Association at Cork, 1843, pp. 60, 61. 

 f Geol, Trans. 2nd Series, vol, v. plate 55. 



