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Scientific Intelligence. 



lower half is very much expanded in the plane of cleavage, and has 

 lost thereby its radiations. In figure 6 there is the same angle between 

 the plane of bedding and dip of cleavage, but a different position of 

 the shell, in consequence of which one-half was extremely shortened, 

 while the other was as remarkably widened. In figure 7 a still more 

 singularly lengthened cast of S. giganteus is shown ; it was from a 

 bed where the cleavage intersected it at an angle of 1° only. The 

 elongated half of the cast of the hinge is here three times the length 

 of the other half, and the hinge area is singularly widened, while a 

 great part of the cast of the body of the shell is lost. Figure 8 repre- 

 sents a specimen (imperfect in the hinge portion) expanded in the direc- 

 tion of its length; although not seen in place, Mr. Sharpe observes that 

 there can be little doubt that the distortion took place in a direction 

 parallel to the dip of the cleavage planes. He concludes from the 

 various facts, .that the existing forms may be accounted for by sup- 

 posing that the rocks in which they are imbedded have undergone com- 

 pression in a direction perpendicular to the planes of cleavage, and a 

 corresponding expansion in the direction of the dip of the cleavage. 

 Mr. Sharpe next considers the uniformity of the strike of the dip over 

 large areas, and its parallelism to the anticlinal axes or the ranges of 

 mountains, a view which we believe was first brought out by Necker. 

 He mentions the long lines of uniform strike of cleavage in North 

 Wales, Devonshire, and Cornwall, and the opposite dip on the different 

 sides of the lines of vertical dip ; and he supports the view presented 

 by Mr. Darwin in his work on South America, that this variation in the 

 dip may arise from the planes of cleavage bending in the direction of 

 great curves more or less abrupt. He points out two parallel lines of 

 vertical cleavage in North Wales thirty-five miles apart, having a nearly 

 northeast strike, either side of which the dip gradually diminishes. 

 Other similar examples also are pointed out. A relation between the 

 inclination of the cleavage planes and the elevation of the strata is 

 apparent in the beds; the dip of the cleavage is greater the greater 

 that of the bedding, though the two differ much. In North Wales the 

 cleavage planes usually dip 20° or 30° more than the bedding; while 

 in the middle of Devonshire and Cornwall they are less inclined than 

 the bedding. In the following section (figure 9) in Carnarvonshire, 



Figs. 9 and 10. 



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North Wales, there are several anticlinal and synclinal axes of the 

 stratification, yet, as shown in figure 10, only one axis of cleavage. 

 The several anticlinal and synclinal axes, excepting the central one, 

 have not influenced the cleavage, which follows uniformly its own 

 direction through beds dipping in opposite directions. " Still there is 

 so much relation between the direction of the cleavage planes and the 

 position of the beds, that we might infer from this section alone, that 

 the cause which produced the cleavage of the rocks had helped to 

 determine the elevation of the beds." 





