Book VIL] TERRESTRIAL FLEXURES. 915 
_ Another variety of more complex structure may be termed the 
Park type, from its singularly clear development in the Park region 
of Colorado. In this type an axis of ancient crystalline rocks— 
granites, gneisses, &c.—has been as it were pushed throveh the 
flexure, or the younger strata have been bent sharply over it so that 
after vast denudation their truncated ends stand up vertically along 
the flanks of the uplifted nucleus of older rocks (Fig. 432). 
There may be only one dominant flexure, as in the case of the 

Fie. 432.—Park TYpe of FLEXvrRe. 
a, Crystalline rocks; b, Mesozoic rocks. 
Uinta Mountains, the long axial line of which is truncated at the 
ends by lines of flexure nearly at right angles to it. More usually 
numerous folds run approximately parallel to each other as in the 
Jura and Appalachian chains. Not infrequently some of them die 
out or coalesce. Their axes are seldom perfectly straight lines. 
_(¢.) Unsymmetrical Fleaures, where one side of the fold is much 
steeper than the other, but where they are still inclined in opposite 
directions, occur in tracts of considerable disturbance. The steep 
sides look away from the area of maximum disturbance, and are 
more sharply inclined as they approach it until the flexures become 
inverted. Instructive examples of this structure are presented by 
the Jura Mountains and the Appalachian chain. In these tracts it 
is observable that in proportion as the flexwres increase in angle of 
inclination they become narrower and closer together, while, on the 
other hand, as they diminish into symmetrical forms, they become 
broader, flatter, and wider apart, till they disappear (Figs. 239, 433). 
NEAR LAKE 
CHAUX DU 
DomBirr. St, CLAUDE. V ALSERINE, GENEVA. 

Fic. 433.—SrctTion AcRoss WESTERN* PART OF JuRA MOUNTAINS, 
(After P. Choffat, 5,155, A. Heim, Mechanism. Gebirgsb. Pl. xiii.) 
(d.) Reversed Flexwres, where the strata have been folded over 
in such a way that on both sides of the axis of curvature they dip 
in the same direction, occur chiefly in districts of the most intense 
plication, such as a great mountain chain like the Alps. ‘The ineli- 
nation, as before, is for the most part towards the region of maximum 
disturbance, and the flexures are often so rapid that after denudation 
of the tops of the arches the strata are isoclinal, or appear to be 
dipping all in the same direction (p. 518). A gradation can be 
traced through the three last-named kinds of flexure. The inverted 
or reversed type is found where the crumpling of the crust has been 
greatest. Away from the area of maximum disturbance ee folds 
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