7 
concerned is necessarily volcanic may be questioned. The 
absence of superficial traces of volcanic agency over large 
areas of contorted strata — the limestone district of Craven, 
for example — is not easily reconciled with the views derived 
by Hall from his instructor, Hutton. We must also 
emphatically dissent from his tacit assumption that the 
contorted rocks must have been "in a soft but tough and 
ductile state." Distorted fossils, crystals and pebbles cannot 
well have been soft when they were pinched and bent out of 
shape. 'Not need we assume such a condition during the 
formation of ordinary curved strata. The mechanical pro- 
perties of limestones and other rocks, dry and at ordinary 
temperatures, are such as in themselves satisfy the conditions 
of the problem. 
In 1866 I began some simple experiments, taking up the 
points that had been disregarded by Hall. First of all, I 
took a thin slab of marble and placed it on the edge of a 
mantelpiece, so that the end projected. A few books kept 
the slab in its place, and then I placed a letter weight of one 
ounce on the free end and left it for some weeks. On testing 
it by a straight edge it was found to be deflected to a trifling 
extent. Other plates of difierent materials, two or three 
inches long and as thin as possible, were next procured and 
subjected to the same treatment. But no accurate results 
were obtained, and the form of the experiment was incon- 
venient. 
Subsequently I tried an improved plan. Two wooden 
slabs, ten inches by four, were fitted together by a hinge so 
that they could be set at any angle from 0° to 180'', just as 
you might open a book, keeping the letterpress always down- 
wards. One slab was screwed to the table, the other could 
be adjusted at pleasure. The angle made by the two sur- 
faces was indicated by a graduated semicircle. Upon the ridge 
various thin plates of stone were placed and attached at one 
