OUTLINE OF PRINCIPAL RESULTS. 
In the Iron Springs district of southern Utah, described in this 
paper, sediments of Carboniferous, Cretaceous, and Tertiary ages have 
been intruded by large masses of andesite taken to be laccoliths. 
Erosion following the intrusion developed mountains out of the lac- 
coliths, with surrounding rings of outward-dipping sediments on the 
lower slopes. Later extrusion of lavas covered the eroded lac- 
coliths and sediments. Subsequent erosion has reexhumed the 
laccoliths and part of the sediments, leaving the lavas in a sur- 
rounding zone. The lower slopes and flats adjacent to the lac- 
coliths are covered by the usual unconsolidated deposits of the 
Great Basin country. Faulting, principally of the tension type, is 
prevalent. 
The iron ores constitute (1) fissure veins in the andesite, (2) fis- 
sure and replacement deposits along the contact of the andesite 
with the Carboniferous limestone, and (3) breccia cement in the 
Cretaceous quartzite. The larger deposits are the ones along the 
limes tone-andesite contact. Their longer diameters in general fol- 
low the contact with rough lens shape, but there are many irregular- 
ities due to faulting and other causes. 
About 1,600 exploration pits have been sunk, but the deepest 
goes clown only 130 feet, and has not reached water level. The 
vertical dimensions of the deposits are therefore unknown. Their 
total area is 5,430,000 square feet, and their total tonnage, so far 
as can be measured by area and pits, is about 40,000,000 tons. Prob- 
ably this estimate is much too small, for the pits do not go to the 
bottom of the deposits. 
The ore is magnetite and hematite, containing a small amount of 
limonite. Much of it runs above 60 per cent in iron, but the average 
is about 56 per cent. Phosphorus is uniformly high. Sulphur, 
copper, and titanium are not present in prohibitive amounts. There 
is no evidence of increase in sulphur with depth, but water level has 
not been reached by the pits. The texture is hard and crystalline 
at the surface; beneath the surface the ores are relatively soft. 
The gangue is principally quartz or chalcedony near the surface; 
with depth calcite increases. Garnet, diopside, apatite, mica, 
hornblende, and other silicates constitute minor constituents of the 
ore. 
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