55 • 



press them equally in a direction parallel to their surfaces. The shell 

 will then be compressed in the same direction, so that, generally, the 

 ratio of the length to the breadth of the shell will be altered, but 

 without that twisting which will characterize the distorted form in 

 the former case. In the case of this paragraph, the direction of 

 compression will coincide with what has been above termed a prin- 

 cipal direction, and it will also be that of maximum normal pressure. 

 In the previous case, the common surface of the two beds will be the 

 plane of maximum tangential action. 



If, then, in any stratified mass, we observe the organic remains to 

 be regularly distorted, and twisted from their original forms, as above 

 described, we may conclude that the planes of stratification have 

 nearly coincided with those of maximum tangential action ; but if, on 

 the contrary, the distortion consists only in compression of the shells 

 in a given direction along the surface of the bed where they are 

 found, we may conclude that the direction of maximum normal pres- 

 sure has nearly coincided with this direction of compression, and was 

 consequently parallel to the planes of stratification. The masses in 

 which distorted remains have been found, are generally those which 

 have been much disturbed. The disturbing forces are those to which 

 the distortions are to be referred ; and it may be remarked, that in 

 such cases the directions of maximum and minimum pressure at any 

 point would probably lie in a plane perpendicular to the strike of the 

 elevated beds, and that consequently the planes of maximum tan- 

 gential action, which bisect the angles between those directions, 

 will have approximately the same strike as the beds themselves. 



The bearing of these conclusions on the question of laminated 

 structure is easily seen. Suppose the planes of lamination are ob- 

 served 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 subjected, it is to tangential action, and not to direct pres- 

 sure, that the effect is attributable. Again, if the planes of lamina- 

 tion 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 dis- 

 torted 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 compression 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 col- 

 lected 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 generally 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 



