124 ON THE FLEXURES AND 



the water necessary to their flexibility. If it has not been 

 oftener observed in rocks, it is because we have rarely 

 any access to them except near the surface where 

 they have already lost their water, or because we can 

 not procure and examine them within the time ne- 

 cessary to prevent that change from taking place. 

 But it is, in fact, known that many are not only soft, 

 but partially flexible, when wet or first procured from 

 the quarry. This softness indeed occurs in so many 

 rocks, that it is almost unnecessary to point out ex- 

 amples of it. The deep-seated granite veins in the 

 quarries of Rubislaw near Aberdeen, are not only 

 flexible, but so soft as to receive an impression, 

 becoming hard after exposure to air. The well- 

 known limestone of Sunderland is flexible. In Sky, I 

 have seen a sandstone which could be moulded like 

 dough when first found: and there is a sandstone 

 from China, known to mineralogists, which may be 

 compressed by the hand when immersed in water. 

 There is no difficulty in understanding how beds of 

 clay may have been bent without losing their laminar 

 form; and if shales are the produce of these, as 

 cannot be doubted, they may have been indurated as 

 well after curvature as before it. The extent and 

 value of this argument needs not be pursued; nor 

 needs it be inquired how far the addition of heat, if 

 heat has in these cases been present, might facilitate 

 the flexion of strata not yet indurated. 



Thus it is probable that strata formed under water 

 may have once been flexible: it is probable that many 

 of those which are out of our reach are still capable of 

 admitting curvatures: and it is probable that the pre- 

 sence of water alone is sufficient to fulfil the requisite 

 conditions. 



