98 J. LeConte—Structure and Origin of Mountains. 
Powell (fig. 4), and of the north and south monoclinal ranges 
(ridges) in the Basin-region described by Gilbert and Howell 
(fig. 5). These mountains are evidently formed by the break- 
ing down of a great arch (geanticline). Perhaps the arching 
and the breaking down may have gone on together pari passu. 
But in any case, certainly the whole arch must be regarded as a 
monogenetic upheaval and therefore corresponds to what I have 
called a Range, and the so-called north and south ranges are not 
ranges but ridges. 
Again: a simple anticlinal fold such as I have described, 
may be greatly modified by metamorphism. This is especially 
apt to be the case if the strata be very thick and the fold be 
narrow and high; that is, if the compression in a given space 
and therefore the heat of compression be very great. If now, 
such a sharp fold, metamorphosed in its deeper strata along the 
line of greatest compression, be subjected to profound erosion, 
it forms a common type of mountain, viz: one consisting of a 
granite or highly metamorphic axis flanked on either side with 
tilted strata corresponding to each other. The early geologists 
held, and many even now hold, that in such cases the granite 
axis was pushed up through 
the broken and parted stra- 
te ta. But it is far more prob- 
mere enn, 
S - bea: a ee ‘Z 
To” pet ra able in all cases, and certain 
VIS °. PO" SERPS OR SY, es. . ’ “ 
SE ee ~ Inmany cases, that the weak- 
ened and _ broken - backed 
anticlinal has been cut away, and the deeper-seated and there- 
fore metamorphic and therefore also harder strata have been 
exposed along the axis, as shown in the ideal section, figure 6. 
2. Mountains of many folds.—We have thus far spoken only 
of mountains consisting of a single anticlinal fold modified by 
metamorphism, by faults and by subsequent erosion. But 
great mountain ranges most commonly consist of many folds, 
alternately anticlinal and syn- 
clinal; either open as the case 
83 = of the Jura or more usually 
Section across Coast Range, from San Closely appressed as in the Ap- 
range of California, as I have shown (this Journ., ii, 297, 1876) 
consists of at least five anticlines and as many synclines closely 
appressed so that fifteen to eighteen miles of original sea-bottom 
is compressed into six miles. As this range may be r 
as the type of this class I introduce here the section used in the 
paper referred to. The structure of the Alps is similar but even 
