508 George Hickling—Folds and Overfolds, 
folds would be asymmetrical, with their steep sides facing away from 
the main synclinal axis, on either side, as indicated in the subjoined 
diagram.} 
Fie. 3.—Showing the distortion of minor folds by the relative displacement of the 
layers in the larger one. 
Let us now assume the lateral compression of the whole area to 
continue. What will be the result? Either the general syncline 
may become deeper, or the minor folds may be accentuated. But, 
since the extent to which a great fold can be raised or depressed is 
limited, the latter result will sooner or later occur, and as the minor 
folds are accentuated they will become overfolds, tending more and 
more to be isoclinal as they are further compressed. It is important 
to notice that the limbs of such wsoclinal folds will dip towards the axis 
of the major syncline, on either side. Here, I believe, we have the true 
explanation of the character of the folds seen so admirably on the 
North Devon coast. 
It is scarcely necessary to add that what has just been said of minor 
folds on synclines will apply equally, with suitable modifications, to 
minor folds on anticlines. In the latter case there will tend to be 
produced more or less isoclinal folds with limbs dipping away from the 
main anticlinal axis. Hence we may conclude as an important general 
rule that the direction of dip of the limbs of a series of isoclinal folds 
indicates the direction of dip of the side of a larger fold on which they 
have been produced. By this means, the former existence of a great 
fold may be inferred when the structure of a district has become so 
complicated that direct evidence of it is obscured or lost. 
For example, if in a great syncline a series of minor overfolds are 
produced on either side as here described, and the crushing still 
continues, it is evident that the sides of the syncline will gradually be 
pushed in under the central portion, and fan-structure will be the 
result. And thus it would seem highly probable that areas presenting 
fan-structure, notwithstanding the fact that they present the general 
features of an anticline, and have, indeed, been aptly described as 
anticlinorums, have originated by the modification of great synclines. 
As my friend, Mr. D. M. 8. Watson, suggested to me, an analogous 
process may help in some degree to explain why hills have so 
frequently a synclinal structure. 
Further, it needs little consideration to show that the direction of 
overthrusts will be governed by the same rule that holds for overfolds, 
1 This modification of the minor folds may be beautifully demonstrated by taking 
a pile of sheets of paper laid flat, drawing symmetrical curves on the edges, and then 
folding the paper. If the paper is folded sufficiently, beautiful isoclinal curves may 
be produced. 
