110 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
sandstones, and that over this and at the top of the lower great 
division is a series of at least three limestones of a semilenticnlar 
character. The lower of these limestones included the largest single 
body of copper ore yet discovered in Bingham. 
The upper great division of the Bingham section, several thousand 
feet in thickness, is made up. in the main of normal quartzite, and 
includes in addition relatively thin calcareous sandstones, calcareous 
carbonaceous shales which occasionally attain a thickness of a few 
hundred feet, and thin blue limestones. No particular horizon in 
this series is of special economic importance. The principal bodies 
known to occur in it, however, are associated with calcareous shales. 
Scanty faunas indicate I he series to be of Upper Carboniferous age. 
Igneous rocks. — Igneous rocks of at least two distinct types and 
ages are recognized. The area studied was too Limited to afford the 
data necessary to prove the origin, source, and direct ion of movement 
of their magmas. Accordingly all statements concerning these sum 
jects must be regarded for the present as in the nature of tentative 
suppositions. In brief, molten masses have been injected into the 
sediments in this area from the lowest nearly up to the highest] 
These broke upward across ami along the beds in an extremely 
irregular manner and cooled in the form of irregular dikes, sills, and 
laccolil hs. 
The petrographic character of this intrusive varies from the fine- ,( 
grained, rather basic porphyry of the laccolith at Upper Bingham tq 
a coarse, slightly more acid type in Keystone Gulch, and to the coarse 
acid type north of Can- Fork toward its headward portion, and finally 
to the altered acid type between Bingham Canyon and Carr Fork. 
For general purposes these maybe considered as several fades of a 
single magma characterized by the occurrence in the Bingham lacco 
lith. Under the microscope thin sections appeared to be augite 
biotite-diorite-porphyry, but chemical analyses show the content of 
potash to exceed considerably the average potash content of diorite 
porphyry and to agree with that of monzonite. Accordingly the rock 
maybe regarded as an intermediate type between diorite-porphy ry 
and monzonite. It occurs chiefly in the lower half of the section, and 
assumes considerable economic significance, first in connection with 
the main limestones, and second as the home of valuable mineral 
deposits. 
The second tj^pe of igneous rock within this area is restricted to the 
lower slopes of the outer extreme eastern part of the range. Petro 
graphically it differs from the intrusive just described in being moil 
acid and allied to the andesites. No positive proof regarding the age 
and origin of this volcanic body has been found. A small prospect, 
tunnel exposes the andesite breccia overlying an old surface debris of 
quartzite similar to that which characterizes the present slopes. 
Accordingly it may be regarded as an extrusive mass which over- 
