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the other axis is but little expanded ; by this means distorted 
images like b and c can be produced at pleasure, merely by 
passing the coin through the rolls in one or other direction. 
The idea that an approximate measurement of the amount of 
compression to which cleaved rocks had been subjected might 
be deduced from calculations based upon the relative dimen- 
sions of normal and distorted fossils, naturally suggested itself, 
and has been followed up by several observers, particularly by 
Professor Haughton, whose conclusions are strikingly corrobo- 
rative of those obtained by other experimenters by totally 
different modes of procedure, as will subsequently be alluded 
to. 
The researches of Mr. Sorby, however, not only advanced 
the previous knowledge of the phenomena of cleavage structure, 
but proved, experimentally and conclusively, that cleavage was 
not in any way connected with chemical, crystalline, or elec- 
trical agencies, and that it was solely the effect of mechanical 
forces acting upon the rock so as not only to effect a consider- 
able compression or condensation of its substance, but at the same 
time to re-arrange or change the position of the particles of 
which the rock is composed. 
One of the most interesting illustrations brought forward by 
Mr. Sorby to show the effect of such compression, is seen in 
fig. 11, PI. LYII., being a vertical section from near Ilfracombe, 
where a bed of very much contorted coarser arenaceous slate is 
seen interposed between two beds of fine- grained well -cleaved slate, 
the stratification lines of which are denoted by the darker bands — 
a, b. An inspection of this section at once renders it apparent 
that these beds, originally deposited as horizontal strata, must 
have been squeezed together from the sides, so as to crumple 
up the non-yielding arenaceous bed, whilst the particles of the 
slate, giving way to the compression, were only packed to- 
gether more closely, and became so much denser than before. 
To use the author’s words, these phenomena are “ analogous to 
what would occur if a strip of paper, for instance, was included 
in a mass of some soft, plastic material, which would readily 
change its dimensions. If the whole was then compressed in 
the direction of the length of the strip of paper, it would be 
bent and puckered up into contortions, whilst the plastic ma- 
terial would change its dimensions without such being the case ; 
and the difference in distance of the ends of the paper, as 
measured in direct line or along it, would indicate the change 
in dimensions of the plastic material.” 
Numerous observations, some of which have been already 
referred to, prove that the arrangement of the particles in 
cleaved rock differs from what it is in normal sedimentary 
rocks, and that in the former the particles composing them 
