Prof. Hughes— Lower Cambrian, Bethesda, N. Wales. 13 © 
back, interrupted, and repeated, in every variety of fold and break— 
of which examples are given in the subjoined woodcut, Fig. II. 
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The selection shows three stages of the same class of movements, 
where the folds are more conspicuous in the first and the faults in 
the last, so that in it portions of the folds are faulted out of the 
field of view altogether. This is not cleavage, nor necessarily con- 
nected with cleavage, and on this distinction 1 would lay particular 
stress. Many rocks, such as the gnarled series of Anglesea and 
parts of the Devonian of Devonshire, show the fault and fold 
structure with inconspicuous cleavage. This is the action which 
produces schistosity in all sorts of rock, modified, of course, by its 
original character, whether, for instance, it is a soft rock with sub- 
ordinate hard beds, or a somewhat uniform mass with veins. The 
essential character of the fold and fault structure being that there is 
a relative displacement of considerable portions of the mass, pro- 
ducing what I have elsewhere called a universal slickenside. The 
essential character of cleavage being that there is no such dis- 
placement of considerable portions of the rock, but only a molecular 
rearrangement producing a tendency to split along an indefinite 
number of parallel planes. 
Cleavage may affect a rock in which the bedding planes are not 
