WATSON — NOTUti ON SIETAIJJFKmidS SADDLES. 
359 
being somciimes mainlaincd over a whole country, although generally 
confined to a comparatively small poi-tion of the strata. It happens 
tliat the contortions, which are not to be confounded with those 
larger etfects of the same kind known as synclinal and anticlinal 
axes, ai'e so complicated that, as in some of the oldest rocks of North 
Wales, the folds are partly turned over, and the order of the strata 
is actually inverted ; but such extreme cases are comparatively rare. 
Tlie countiy where the beds are thus disturbed almost invariably 
displays other proofs of mechanical alteration, and usually more or 
less of elevation. As conducting to the explanation of the dis- 
turbances which may have taken place in a district these phenomena 
are often very useful guides, since they nearly always indicate the 
direction in which the distm-bing force was applied, and tliis I shall 
presently show. 
It may be demonstrated experimentally that plicated or folded 
strata are the result of great lateral pressure, aided by much super- 
incumbent weight. Sir James Hall — whose important experiments 
in uniting chemistry with geology laid out a path which, unfor- 
tunately for the progress of the latter science, in at least one depart- 
ment, has been since too little followed — succeeded admirably in re- 
producing the appearances in the rocks by placing plates of moistened 
clay one over the other, with a heavy weight on the top of them, and 
then squeezing them at the sides. The effect produced is re- 
presented in the diagram (fig. 1), which will also serve as an illus- 
tration of the contortions on the large scale, as in nature. The 
appearances, however, are best imitated by thick paper, or cloth, 
moistened by gum, or other adhesive liquid, which will cause the 
sheets to retain the form they may assume, after the pressm'e is 
withdrawn. It will be observed that a series of consinuous waved 
lines are produced ; in fact, a miniature succession of anticlinals and 
synclinals, and it is one of each, taken separately, that the miner calls 
a saddle (see fig. 2). The crown may be either an unbroken arch 
(ft) (fig. 2), or, if the squeezing and bending has been more severe 
than the rock could stand without fracture, it may be an angle (c), 
more or less acute. From the crown downwards there is usually a 
well marked fissure, or joint, traversing all the beds in succession 
with more or less inclination from the vei'tical (fig. 2, B B'). The 
sides of a saddle are termed its wings, h b' (fig. 2), and the crown is 
called the huckle («) ; the joint dividing the crown is called the 
saddle-joint ( « B, c B'). The space between two saddles at its lower 
part, which on the large scale would be termed a synclinal axis, is 
called the trough (c) (fig. 2), and, as it is usually fractured hke the 
crown, the dividing fissure is called the trough joint, indicated by 
the line d c. 
What I have just described relates more particularly to the hme- 
stone saddles than to the plicated beds of the calcareous and bitu- 
minoiis shales which overlie the limestone, since in the latter, 
although the same general structure prevails, thei'e is more confusion 
in the strata. 
