456 J. M. BOUTWELL 
trough. Into this, and thus blanketing the surface connection of 
these structures, extensive and thick masses of andesite have flowed. 
That portion of this region known as the Park City District is tra- 
versed diagonally by this axis. The sediments in this area have been 
cut, deformed, and altered by a series of intrusives, and andesite flows 
cover the sediments at the northeast. These sediments rim around 
the intrusives and dip off from their flanks. The area thus embraces 
the northeast end of the great composite laccolith of the middle 
Wasatch. 
The broad structure of the formations within the Park City Dis- 
trict proper is that of an anticline pitching northerly. The general 
strike follows the course of a U, the base of the letter being at the 
north. At the center, along the main axis which passes north-north- 
east just east of Park City, occurs an extensive area of Weber quartzite, 
from which the overlying younger formations dip—in general to the 
west side on the west and to the east on the east. Immediately north 
of Park City these strikes converge and unite to form the nose of the 
pitching fold. 
This structure, however, is true only in a general sense, as it is 
greatly modified by minor folding and extensive faulting. Athwart 
this anticline, in a general east-west course, extends a series of intru- 
sive masses. These include the diorite stock of Clayton Peak at 
the extreme southwest, east of this the stocks and dikes of andesite 
porphyry which extend eastward diagonally across this area and 
upward through all sedimentary formations from the Weber to the 
Thaynes, and next beyond to the east extensive thick flows of andesite. 
These are the highest members of the chain of intrusives which lie 
athwart the course of the range at this point. They occupy the 
normal position of sediments, and thus interrupt the general anti- 
clinal structure above described to only a minor degree by local folding. 
Three great systems of fracturing and faulting further break the 
broad structure, trending north-south, northeast-southwest, and north- 
west-southeast (east-west), respectively. 
One of these fracture systems cuts across the nose of the anticline 
on its northeast side as a north-south line of dislocation, which is 
marked by the eastern inclosing wall of Deer Valley Meadow and 
Frog Valley. Along this fault the displacement has been such that 
