118 Mr W. Hopkins on the Internal Pressure of Rocks. 



directions, will have approximately the same strike as the 

 beds themselves. 



The bearing of these conclusions on the question of lami- 

 nated structure is easily seen. Suppose the planes of lami- 

 nation are observed to be nearly coincident with those of 

 stratification, and that the distortion of the organic remains 

 consists in their being twisted from their primitive forms. 

 Then, if the position of the planes of lamination has been due 

 to the internal pressures to which the mass has been sub- 

 jected, it is to tangential action, and not direct pressure, that 

 the effect is attributable. Again, if the planes of lamination 

 have nearly the same strike as the beds, and are inclined to 

 them at an angle of about 45°, while the organic remains 

 have been distorted only by direct compression, the planes of 

 lamination must, in this case, also have coincided with those 

 of maximum tangential action, and we shall have the same 

 conclusion as in the former case. The direction of compres- 

 sion of the organic forms ought, according to this view, to be 

 perpendicular to the intersections of the planes of lamination 

 and those of stratification. 



Mr Sharpe, in a paper recently published in the Journal 

 of the Geological Society, has stated nearly all the evidence 

 hitherto collected on this subject ; and it appears, that the 

 organic bodies are most twisted from their original forms in 

 those cases in which the planes of lamination coincide most 

 nearly with those of stratification, and that they have gene- 

 rally suffered most direct compression without twisting, in 

 those cases in which the planes of lamination are inclined to 

 those of stratification, at an angle of 40^ or 50". We must 

 therefore conclude, according to the last paragi'aph, that the 

 planes of lamination approximately coincide with those which 

 were formerly the planes of greatest tangential action. 



The author does not regard this mechanical action as the 

 probable primary cause of the laminated structure, but rather 

 as u secondary cause, which may have had its influence in 

 determining the positions of the planes of lamination. He 

 trusts that further evidence will be collected on the subject 



