SOUTHERN WASATCH MOUNTAINS, UTAH 449 
N.-S. trend and a series of N.-S. and E.-W. block faults of the Basin 
Range type (see Fig. 4). The former are so poorly exposed, their 
courses so nearly parallel to the N.-S. system of the block faults, and, 
in some places, the rocks along them so free from severe crumpling 
or crushing, that the writer is not fully convinced of their over- 
thrust character. 
Overthrusts: East of Santaquin the northern part of the pre- 
Cambrian granite appears to overlie quartzite, but the contact is 
concealed by float. A little farther northward, however, the granite 
pinches out and the main body of Cambrian quartzite overlies a 
dark brecciated limestone, which passes downward into shale 
and quartzite. This lower quartzite exposure, in turn, overlies 
fossiliferous Mississippian limestone, which is very free from any 
of the crumpling or brecciation which is likely to accompany over- 
thrusting. The Mississippian limestone is underlain conformably 
by fossiliferous Cambrian shale and a third quartzite exposure. 
The pre-Cambrian granite southward disappears beneath a high 
alluvial fan which is now trenched by Santaquin Creek; but the 
main Cambrian quartzite body continues, and at its southernmost 
exposure rests again upon fossiliferous Mississippian limestone, 
which, as in the other instance, is surprisingly free from contortions 
and crushing. So far as the positions of the rocks are concerned, 
reverse or overthrust faulting seems the only interpretation; 
but the absence of disturbance in the overridden limestone is not 
easily explained. 
At the mouth of Green Canyon, 8 miles south of Santaquin, an 
extremely brecciated and, so far as seen, non-fossiliferous limestone 
dips eastward beneath Cambrian quartzite, and here is the most 
convincing evidence of an overthrust, although time did not permit 
a thorough study of the immediate contact. A tunnel of the 
Excelsior Mining Company has been driven through the limestone 
into the quartzite, but the entrance to it was locked at the time of 
the writer’s visit. No fossils were found in the underlying lime- 
stone, but the presence on the dump of fragments of a highly 
carbonaceous and finely pyritic bed, similar to two found elsewhere 
in the Mississippian of the southern Wasatch Mountains and of 
the Tintic district, gives a clue to the age of the limestone, and 
