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EXPERIMENTAL RESEARCHES ON THE 
CONTORTION OF ROCKS. 
By L. C. MIALL, 
CURATOR TO THE LEEDS PHILOSOPHICAL SOCIETY. 
[PLATE LXXX.] 
T HE geologist is continually engaged in attempting to repro- 
duce a past world. From footprints lie tries to reconstruct 
extinct animals ; from accumulated sediments lie infers the 
course of ancient rivers. He seeks to interpret fissures and 
veins, cliffs and valleys, by referring them to natural agents 
whose mode of operation is comprehensible. In general, from 
effects he reasons to causes. 
No doubt this process is liable to continual error. The 
candid geologist will perhaps admit that, biologists excepted, 
no scientific inquirers have blundered so often and have so 
often been forced to relay the foundations of their labours as 
the students of physical geology. The extreme complexity of 
the phenomena concerned explains the natural tendency of 
geologists to guess instead of demonstrating. 
The only remedy for this source of error is continual veri- 
fication. When we have assigned a cause to any group of 
effects we must endeavour to show by tangible evidence that 
the cause invoked is actually existent, not wholly conjectural, 
and that it is adequate to the work hypothetically attributed 
to it. 
It needs hardly be said that this process of verification is 
usually tiresome, and sometimes impossible. We cannot always 
imitate, even upon the smallest scale, operations which have 
played a great part in the history of the earth. Even where 
verification is easy we are too prone to neglect it, and trust to 
assumption or the application of formulae. Our present subject 
of Contortion of Rocks is but one out of many branches of 
physical geology which has been overlaid with speculation, 
while the recorded experiments are few. 
