DESCRIPTIVE GEOLOGY. 19 
The general strike in the southern part of the section is about 
N. 50° E., and it is instructive to note that the direction of structure 
so strongly emphasized topographically in the Alaska Range is here 
repeated. In the northern part of the section the strike is more 
nearly east and west. The rocks are closely folded and in most cases 
their attitude is nearly vertical. There is a distinct symmetrical 
arrangement with reference to a northeast-southwest axis. and. so far 
as our present knowledge extends, this symmetrical disposition of the 
rocks seems to be a fact of importance in regard to their structure 
and succession. This repetition is most noticeable in the occurrence 
of limestone. The limestones of the White Mountains, with associated 
greenstones, flanked on the nortliAvest by red and black slates and 
prominent masses of impure quarzite, are repeated 15 miles to the 
north in another limestone belt, less conspicuous topographically than 
that of the White Mountains, with a similar association of rocks, and 
flanked on the northwest by similar slates and quartzites. The rocks 
of the middle portion of the section are slates, greenstones, and cherts, 
and, although the relations are not clear, there are two main areas 
of cherts about 3 miles apart, with black, purple, and greenish 
slates and some greenstones in the intervening space. North of the 
northern belt of cherts, toward the northern belt of limestones, there 
:ire conglomerates containing abundant chert pebbles. Farther south, 
toward the limestones of the White Mountains, there are also chert 
conglomerates with pebbles an inch or more in diameter, associated 
with finer rocks containing grains of chert and fragments of slate. 
Black slates are also common and thin beds of conglomerate are inter- 
bedded with them. The slates are closely succeeded by the limestones 
on either side, and although the direct relation of the two kinds of 
rock was not observed, it is believed that the limestones are younger 
than the rocks above described. The quartzite flanking the limestone 
on the north, which is very similar to other quartzites apparently in- 
terbedded with the limestones, contains occasional fragments of chert, 
and it seems best until further knowledge is available to consider 
the flanking slates and quartzites as partly of the same age as the lime- 
stones and partly younger. 
Fossils found in the limestones of the White Mountains have been 
determined as characteristic of early to middle Devonian, and some 
of them are possibly of Silurian age : but t he si rat [graphic associai ion 
makes it probable that all the remains belong approximately to the 
same horizon, and the determinations point more definitely to the 
Devonian. No fossils were found in the limestone^ of the northern 
belt, but the rocks and their associations are very similar, and no 
reasons were found for assigning them to a different position. 
The contact relations of these rocks with the Carboniferous rocks 
north of them and the nietainorphics south of them are not clear. 
