HINTZE, GEOLOGY OF WASATCH MOUNTAINS, UTAH 137 



which is overturned and does not match with the lower beds on either 

 side. All attempts to explain the structure as a syncline, or overturned 

 anticline, fail when the succession of beds is noted, leaving the only rea- 

 sonable basis of explanation that of an overthrust block. 



Faults 



In a region of such complicated structure, faulting may be expected 

 to occur. Dislocations are met with in every mine, but those on a big 

 scale are few in number. Whether large or small, they appear to belong 

 to two systems of fracturing, but movement has probably occurred more 

 than once in each system. The directions of these two sets of fractures 

 are respectively north-east and south-west for those carrying the ores and 

 dikes, and northwest-southeast. These correspond to the dip and strike 

 of the Alta monocline and may therefore be classified as dip faults and 

 strike faults. 



The earliest displacements are those in which the fissure veins carrying 

 the ore were found. These have a fairly constant direction, N. 70° E., 

 and no doubt belong to the same period of fracturing which gave rise to 

 the lode deposits of the Park City district which lie in the path of their 

 northeastward extension. Into some of these, the dikes which are com- 

 mon in the southern part of the district were injected, and it is thought 

 that the ore-bearing solutions came up in others at the same time, or 

 immediately following, depositing the ores. The displacements above 

 this first set of fractures do not appear to have been very great. They 

 are probably more in the nature of great cracks which were formed 

 through the effects of intrusion of the larger bodies of igneous rock to 

 the east and west, as inferred from tlie correspondence of their direction 

 with the general trend of the intrusives. On the other hand, when com- 

 pared with the general dome structure of the region they are radial and 

 might be considered as tension cracks made when the region was thrown 

 into its present arched condition. 



After the formation of the ore deposits of the district in the northeast- 

 southwest fissures, a second period of faulting occurred, having a trans- 

 verse direction to the first set of fractures. This is shown in the north- 

 west-southeast faults encountered in many of the mines, where they in- 

 variably displace the ore bodies. A notable case is the great Atwood 

 "slip" which cut out the ore of the famous Emma mine. Many other 

 examples are known in the various mining properties. 



The displacements of these strike faults are much greater than those 

 of the earlier fractures. The one occurring in Superior Gulch running 

 north into South Fork appears to have the greatest throw and has been 



