6 
geological speculation to the test of actual physical experi- 
ment/' investigated the subject of contortion with much care. 
The curved strata of the Berwickshire coast had engaged his 
attention since the year 1788. In 1814 appeared his remarks 
on "The Convolutions of Strata and their meeting with 
Granite.'^* In this interesting paper he describes the local 
phenomena with some minuteness, and then gives the " rude 
experiment" contrived to imitate the conditions which he 
supposed to have obtained in nature : — 
"Several pieces of cloth, some linen, some woollen, were 
spread upon a table, one above the other, each piece repre- 
senting a single stratum ; a door (which happened to be off 
the hinges) was then laid above the mass, and being loaded 
with weights, confined it under a considerable pressure. Two 
boards being next applied vertically to the two ends of the 
stratified 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 
constrained to assume folds, bent up and down, which very 
much resembled the convoluted beds of killas, as exhibited 
in the crags 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 general effect; 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./' 
The positions which we may now consider to have been 
established by Sir James Hall's experiments and reflections 
are these : That strata originally horizontal have been curved 
and folded ; and that the disturbing force has acted in a 
horizontal direction. His further decision that the force 
* "Transactions Royal Society Edinburgh," vol. viL pt. 1. 
