86 ON THE CONVOLUTIONS OF STRATA, 



tified mass, were forced towards each other by repeated 

 blows of a mallet applied horizontally. The consequence 

 was, that the extremities were brought nearer to each other, 

 the heavy door was gradually raised, and the strata were con- 

 strained to assume folds, (fig. 4. Plate IV.), bent up and 

 down, which very much resembled the convoluted beds of 

 killas, as exhibited in the craggs of Fast Castle, and illustrated 

 the theory of their formation. 



I now exhibit to the Society a machine, by which a set of 

 pliable beds of clay are pressed together, so as to produce the 

 same effect, fig. 5. ; and I trust, that the forms thus obtained 

 will be found, by gentlemen accustomed to see such rocks, to 

 bear a tolerable resemblance to those of nature, as shewn in 

 fig. 6., copied from the forms assumed in the machine, by an 

 assemblage of pieces of cloth of different colours. 



It still remains for us to consider how this horizontal thrust 

 may have been produced. It will be found, I conceive, to 

 arise, as a natural consequence from Dr Hutton's original 

 hypothesis, according to which our continents have been rai- 

 sed from the bottom of the sea, and elevated to their present 

 positions, by the internal action of the same heat which shews 

 itself externally in volcanoes. 



The most obvious mode of investigating these internal ac- 

 tions, in pursuance of the Huttonian view, is to study the ex- 

 ternal volcanic phenomena, and to consider what variations 

 and modifications would be produced upon these last by the 

 circumstances attending the subterranean action of the same 

 powers. 



With this view, I beg leave once more to solicit the atten- 

 tion of the Society, to a scene which I have mentioned in for- 

 mer papers, and to refer to some plates representing it, which 

 I have given in the sixth volume of our Transactions, in my 



paper 



