3 - BY - F Aw 
516 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Boor IV. 
zontal or gently inclined strata in the form of an abrupt inclination, 
and then an immediate resumption of the previous flat or gently - 
sloping character. The strata are thus bent up and continue on the 
other side of the fold at a higher level. Such bends are called 










































































































































Fic, 235.—Curvep SILURIAN Rocks oN THE Coast oF BERWICKSHIRE. 
Monoclines or monoclinal folds, because they present only 
one fold, or one half of a fold, instead of the two in an arch or trough 
(Fig. 255, Section 1). The most notable instance of this structure in 
Britain is that of the Isle of Wight (Fig. 236), where the Cre- 

Fic. 236.—Sxrorion or A Monoontinat Foup, [ste or WIGHT. 
taceous rocks (c) on the south side of the island rapidly rise in 
inclination till they become nearly vertical, while the Lower 
Tertiary strata (¢) follow with a similar steep dip, but rapidly 
flatten down towards the north coast. Probably the most gigantic 
monoclinal folds in the world are those into which the remarkabl 
horizontal and undisturbed rocks of the Western States and territories — 
of the American Union have been thrown.* : 
From the abundance of inclined strata all over the world we may 
readily perceive that the normal structure of the visible part of the 
earth’s crust is one of innumerable foldings of the rocks. Some- 
times more steeply, sometimes more gently undulated, not infre- 
quently dislocated and displaced, the sedimentary accumulations of 
former ages everywhere reveal evidence of great internal movement. 
Here and there the movement has resulted in the formation of a 
1 See Powell’s “Exploration of the Colorado River of the West,” and “ Geology of 
the Uintah Mountains,” in the Reports of the United States Geographical and 
Geological Survey. 

