448 G. F. LOUGHLIN 
conglomerate, part of which consists of quartzite, chert, and lime- 
stone pebbles, and part of calcareous beds full of peculiar concretion- 
ary growths. Some of these concretions resemble shells in form, 
and one undoubted gastropod was found, which Dr. T. W. Stanton 
of the Survey says may be a fresh-water Eocene species. The 
unconformity implies the removal by erosion of the Weber quartz- 
ite, the Park City formation, and the Mesozoic formations which 
overlie these formations in the Park City district. Overlying the 
Eocene conglomerate is a coarse andesitic (or latitic) breccia. Its 
outcrops are weathered and largely reduced to aggregates of loose 
cobbles some nearly a foot in diameter, and the nature of its con- 
tact with the underlying conglomerate, whether conformable or 
unconformable, could not be determined.t Intrusive volcanic 
rocks are limited to a few dikes, also of andesitic or latitic character. 
In the low hills south and southwest of Santaquin, a veneer of 
Eocene conglomerate with remnants of the volcanic breccia over- 
lies limestones of pre-Mississippian (probably Cambrian) age, and 
35 miles farther southwest, in the Sevier River Canyon, the same 
Tertiary sequence of rocks rests unconformably upon the Cambrian 
quartzite. Nearly the whole Paleozoic, as well as the Mesozoic, 
section in central Utah is thus beveled off by this unconformity, as 
is the case in the Uinta Mountains in northeastern Utah.? 
The last two Eocene occurrences mentioned are somewhat 
farther west and north than any previously mapped, and it is 
believed that they are not far from the original limits of the Eocene 
in this region; for in Long Ridge and the East Tintic Mountains, 
about 12 miles southwest of Santaquin, the same type of andesitic 
breccia rests either directly upon Paleozoic rocks, or is separated 
from them by an intervening body of effusive rhyolite, and no sedi- 
mentary rocks later than Paleozoic have been found. 
Structure.—The principal structural features in the Santaquin— 
Mount Nebo district are faults, including doubtful overthrusts of 
™C. K. Leith and E. C. Harder. (Bull. U.S. Geol. Survey, No. 338 (1908), pp. 18 
and 21) have proved an unconformity between Cretaceous and Eocene beds in the 
Iron Springs district of southern Utah and a later unconformity between the Eocene 
beds and Miocene lavas. 
2F. C. Weeks, op. cit., p. 442. 
