boutwell] PARK CITY MINING DISTRICT, UTAH. 37 
and the probable age of the larger divisions are as follows: (1) lime- 
stones of improved thickness, probably of Lower Carboniferous age; 
(2) 1,500 feet of massive normal quartzite, unfossiliferous, probably 
of Upper Carboniferous age; (3) 590 feet of calcareous beds, mainly 
blue limestone, with some shale, of Carboniferous age; (4) 1,100 feet 
of red shale and sandstone, probably of Mesozoic age; (5). 450 feet of 
calcareous sandstone, interbedded limestone, shale, etc., Mesozoic; 
(6) 140 feet of red shale, Mesozoic; (7) 630 feet of limestone, calca- 
reous sandstone, and gray shale, Mesozoic; and (8) an unproved thick- 
ness of red shale, Mesozoic (?). 
The correlation of members of this series throws light upon their 
relation to the ore-bearing rocks in neighboring mining regions. The 
lowest limestones here may be tentatively correlated with those on the 
divide north of Alta and with those which underlie the main ore- 
bearing series at Bingham. Accordingly the main quartzite of Park 
City may be tentatively correlated with the great quartzite series in 
lower Weber Canyon in the vicinity of the railroad tunnels and with 
the main quartzite at Bingham. Valuable data upon the geological 
history of this region have been secured in the course of this strati- 
graphical study. They will not be considered in the present abstract, 
however, since the character of the country rock is of more direct 
economic interest. 
Igneous rocks. — Within this area igneous rocks of three types have 
been found — a fine, even-grained dioritic type, a coarser porphyritic 
type, and a poorly defined type which ranges from andesitic to basaltic 
facies. The first two are intrusive in origin; the last, so far as it may 
be judged from the present incomplete data, is extrusive or volcanic 
in origin. 
The origin of these rocks bears directly upon two in'actical matters 
of deep importance to mining men — the extent and the origin of ore. 
The extrusive or volcanic rocks (those which flowed out upon the 
surface) are often found to be in the form of a blanket overlying the 
country rock, and as such would not be expected to lead to ore forma- 
tion nor to truncate in depth previously formed ore bodies. The 
intrusive masses, however, having reached their present positions and 
forms through injection in the state of a semiliquid pasty magma into 
the sedimentary country rock, may reasonably be expected both to 
have generated ore and to have truncated any previously existing ore 
bodies which lay in their paths. That is to say, the intrusions of 
diorite and diorite-porphyry do not underlie the sediments as a foun- 
dation of older rocks, nor do thej^, like the extrusives, overlie the 
sediments, but they break irregularly across the sediments from bed 
to bed. When the molten magma came in contact with certain lime- 
stones, it led to the formation of various secondary minerals, and in 
those limestones which possessed suitable comrjosition it may have 
induced the formation of ore. 
