Experimental folding

Saturday, November 23, 1996

J. Hall, Transactions of the Royal Society of Edinburgh, 7:85 (1815)

I endeavoured to illustrate my idea by the following rude experiment, made with such materials as were at hand. Several pieces of cloth, some linen, some woollen, were spread upon a table, one about the other, each piece representing 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 (Fig. A), 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 (Fig. B), 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. C); 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, copied from the forms assumed in the machine, by an assemblage of pieces of cloth of different colours.

folding diagram showing 3 steps