84 ON THE CONVOLUTIONS OF STRATA, 



In reducing these irregular forms into system and connec- 

 tion, one object, of no small consequence in geology, seems to 

 be obtained ; but it would be desirable, if possible, to go a step 

 farther, and to discover by what means this peculiar arrange- 

 ment has been brought about. For this purpose, it will be 

 necessary to shew, first, That this peculiar conformation may 

 be given to a set of horizontal beds by a mechanical force of 

 sufficient strength ; and, secondly, That there are rational 

 grounds for believing, that such a force has been actually 

 exerted in this case. I have now, and formerly, tried to esta- 

 blish the first point by experiment ; and I shall endeavour to 

 vindicate the second by a train of geological reasoning, found- 

 ed upon some volcanic phenomena. 



In the year 1788, when I had the pleasure of visiting the 

 coast of Berwickshire, in company with Dr Hutton and Mr 

 Play fair, it occurred to me, that this peculiar conformation 

 might be accounted for, by supposing that these strata, origi- 

 nally lying flat, and in positions as nearly level as might be 

 expected to result from the deposition of loose sand at the 

 bottom of the sea, had been urged when in a soft, but tough 

 and ductile state, by a powerful force acting horizontally ; that 

 this force had been opposed by an insurmountable resistance 

 upon the opposite side of the beds, — or that the same effect 

 had been produced by two forces acting in opposite direc- 

 tions ; at the same time that the whole was held down by a 

 superincumbent weight, which, however, was capable of being 

 heaved up by a sufficiently powerful exertion. 



By either of these modes of action, I conceived, that two 

 opposite extremities of each bed being made to approach, the 

 intervening substance, could only dispose of itself in a succes- 

 sion of folds, which might assume considerable regularity, and 

 would consist of a set of parallel curves, alternately convex and 



concave 



