22 
POPULAK SCIENCE KEVIEW. 
In this paper I propose to give results of experiments under- 
taken in the hope of verifying some generally received prin- 
ciples of geology. It will appear, I think, that we can imitate 
successfully — though on the humblest scale — those great bends 
and folds of strata which the geologist studies with admiration 
at Holyhead or Torquay or Fast Castle. 
A thick solid bed of limestone bent to a right angle without 
fracture — how can that phenomenon have been produced? 
Such was the question which forced itself upon my notice some 
years ago when collecting facts respecting a series of anticlinal 
elevations in Craven. In a limestone quarry at Draughton, 
between Skipton and Bolton Abbey, I came upon beds of 
rock a foot or two in thickness bent into the figure of an 
inverted W. The angles were sharp and unbroken. You 
might pass your finger over the apex of one to make sure that 
there was neither crack nor vein. To what force must we 
assign this disturbance without fracture of strata once hard 
and horizontally laid ? 
Forty years ago it would have seemed natural to invoke a 
volcanic eruption acting upon plastic matter — to regard such 
folds and contortions as due to the formation or elevation of a 
kind of blister upon the earth’s surface. But thanks to a few 
experimental inquirers, such as Sorby, Hodgkinson, and Tyn- 
dall, a number of plausible suppositions had been swept away 
as fallacies. In 1867 the geologist looked rather to lateral 
pressure (due possibly to contraction of the figure of the earth) 
as most probably the force concerned, and he did not find it 
necessary to suppose that the distorted rocks had ever been 
plastic. It is true that Sir James Hall assumed that the rocks 
of Berwickshire were ductile when contorted, and Hr. Edward 
Hitchcock, a well-known American geologist, had recently 
maintained that some contorted pebbles in a conglomerate at 
Newport, Bhode Island, must have been as plastic as moist clay 
when they were bent and twisted. But this gratuitous assump- 
tion was soon disposed of. There were a few fossils in the 
Draughton limestone, and these were distorted like the rest of 
the rock. 
This seemed to prove that plasticity was not a necessary con- 
dition of contortion. The shells and corals had surely not been 
plastic. Indeed the matrix itself may well have been compact 
rock from the time of its deposition, growing by the addition of 
hard lumps and shells and films of stony calcareous matter. 
A rigid body compressed without fracture into the figure of 
W — was this possible ? There is, as I afterwards discovered, a 
source of error in the word “ rigid ” — a latent hypothesis which 
turns out to be erroneous. “ Bigid ” is purely a relative term. 
Stone is rigid in comparison with clay, but plastic in com- 
