AND THEIR MEETING WITH GRANITE. 97 



BELL, whose recent death is much to be lamented). The 

 strata there described occupy a great extent of coast, near- 

 ly forty miles; they consist of strata of slate and limestone, 

 sometimes alternating, and seem to belong to the class of 

 killas. Their convolutions are less elevated and less abrupt 

 than those we have been describing, but in all other respects 

 exactly resemble them. One circumstance is mentioned by 

 the author as a simple fact, and without view to theory, but 

 which seems, in a striking manner, to accord with what we 

 have endeavoured to establish. " Where the strata (he says) 

 " consist chiefly of limestone, with few, or very thin stra- 

 " ta of slate intervening between them, the thickness of a 

 " stratum is frequently five or six times greater at the sum- 

 " mit of the wave, and at the hollow where it begins ascend- 

 " ing to form the next wave, than at the intermediate point, 

 " where the contrary flexure takes place." 



I recollect no such difference as to thickness among our 

 strata; but the circumstance might be expected, upon our theo- 

 ry, to take place, when the beds acted upon by the horizontal 

 thrust were not only flexible and tough like cloth, but also 

 ductile, and capable of being elongated by pressure. For 

 supposing the thrust to have continued, after the folds had, to 

 a certain extent, been accomplished, it is evident, tliat the ho- 

 rizontal pressure acting in some degree at right angles to the 

 beds, where the contrary flexures took place, and of course 

 where their position was most erect, would tend to elongate 

 and thin them at those places, and would have a contrary ef- 

 fect, if any, at the summit and hollow of each arch, where the 

 stratum for a short space occupies an horizontal position. 

 This unexpected fact tends then, I conceive, in a striking 

 manner, to confirm our theory. 



Vol. VII. N When 



