.Ch. v.] experiments to illustrate cueved strata. 



49 



on the east coast of Scotland, where the rocks consist principally of a 

 bluish- slate, having frequently a ripple-marked surface. The undulations 

 of the beds reach from the top to the bottom of cliffs from 200 to 300 



Curved strata of slate near St. Abb's Head, Berwickshire. (Sir J. Hall.) 



feet in height, and there are sixteen distinct bendings in the course of 

 about six miles, the curvatures being alternately concave and convex up- 

 wards. 



An experiment was made by Sir James Hall, with a view of illus- 

 trating the manner in Avhich such strata, assuming them to have been 

 originally horizontal, may have been forced into their present position. A 

 set of layers of clay were placed under a weight, and their opposite ends 

 pressed towards each other with such force as to cause them to approach 

 more nearly together. On the removal of the weight, the layers of clay 

 were found to be curved and folded, so as to bear a miniature resemblance 

 to the strata in the cliffs. We must, however, bear in mind, that in the 

 natural section or sea-cliff we only see the foldings imperfectly, one part 

 being invisible beneath the sea, and the other, or upper portion, being 

 supposed to have been carried away by denudation, or that action ofr 



Fia 64 



water which will be explained in the next chapter. The dark lines in, 

 the accompanying plan (fig. 64) represent what is actually seen of the 

 strata in part of the line of cliff alluded to ; the fainter lines, that por- 



