PROCEEDINGS, 1871 — 1877. 
351 
under what conditions rocks once hard and laid horizontally, could be 
bent to an acute angle without fracture. Sir James Hall, in the 
early part of the century, had made some experiments to imitate the 
condition which he supposed to have resulted in the contorted strata 
on the Berwickshire coast. He placed pieces of cloth of various kinds 
on a flat surface, over which was placed a board loaded with weights. 
Pressure was then applied to each end of the layers of cloth, so that 
they were constrained to assume folds bent up and down, which very 
much resembled the convoluted beds on the coast. The result of 
these experiments seemed to prove that strata, originally horizontal, 
had been carved and folded, and that the disturbing force acted in a 
horizontal direction. He further considered that this force was 
accompanied by some volcanic action, but so far as the contortions in 
the Craven district are concerned there is no evidence of .volcanic 
agency having been an accessory. Mr Miall's experiments were con- 
ducted on thin slabs of various rocks, four inches by three, and 
having a thickness of '07 of an inch. After several experiments, 
he constructed a machine, in conjunction with Mr. Thomas Prince, of 
Bradford, by which pressure could be applied to these slabs conjointly 
and continuously for a period reaching over several months. Slabs 
of limestone and sandstone could be bent to a considerable angle 
without fracture ; but, on the pressure being removed, cracks slowly 
extended themselves across the part where the deflection was greatest. 
Thin plates of Mountain Limestone, especially the bituminous kind, 
proved indefinitely plastic, and it may be doubted whether there is 
any limit to the bending which a careful and patient observer could 
produce in them. Flagstone could be bent to a certain extent, but 
slate was very intractable. The frequent destruction of the plates by 
spontaneous fracture, when removed from the machine, seemed to indi- 
cate that unbroken anticlinals and synclinals are only formed under 
a considerable weight of subjacent strata, and to test this proposition 
Mr. Miall embedded the thin slabs of limestone in pitch, and fitted 
them into a cast-iron box, the two sides of which were removed so 
that horizontal pressure could be applied to the edges of the plates of 
rock. This arrangement proved successful, and slabs nine inches 
long were bent until they rose two-thirds of an inch in the centre. 
