54 IRON ORES OF IRON SPRINGS DISTRICT, UTAH. 
diopside present; (2) red trachyte with grayish-white bands; (3) 
gray and red trachytes, slightly banded in places; (4) gray tuffa- 
ceous trachyte; (5) hard, dense red trachyte. These phases differ 
only in texture, the phenocrysts (mainly sanidine, subordinately 
plagioclase, biotite, and magnetite) being the same throughout the 
series with the exception that layer 5 contains a few pyroxenes, and 
biotite and magnetite are slightly more abundant than in the other 
layers. There is also a slight variation in the amount of plagioclase 
in different parts of the latest trachyte bed. 
Outside of the eastern Antelope Range area only layers 1 and 2 
and perhaps 3 are present. In the eastern part of the Antelope 
Range area layer 2 is comparatively thin, but throughout the rest 
of the quadrangle it forms almost the entire thickness of the bed, 
although the banding is not always as conspicuous as it is here. The 
black pitchstone is nearly always present at its base. At the top of 
the bed in other parts of the quadrangle there is often a layer of less 
distinctly banded material which may represent layer 3. The absence 
of the upper layers is probably due to nondeposition, since erosion 
could hardly have taken place so uniformly over the region as to 
leave practically the same thickness of trachyte throughout. 
The latest trachyte of the Antelope Range (layer 2) is a reddish 
porphyritic rock, with parallel bands of white and gray material 
averaging generally less than one-eighth inch in thickness. The 
phenocrysts, averaging about one-sixteenth of an inch in diameter, 
form about one-tenth of the rock and are largely sanidine. At the 
surface these have been entirely leached out, leaving only the cavi- 
ties. Biotite is also present, being generally altered to phlogopite 
and often entirely decomposed to ferrite. Phenocrysts appear to be 
present in both the gray and red bands. Nearly all the sanidine 
shows Carlsbad twinning. In general, they appear to be quite 
fresh, showing alteration only on the surface and along fractures. 
The alteration products appear to be calcite, kaolin, and quartz. 
The sanidine frequently has inclusions of zircon and apatite. A 
little plagioclase, variety andesine, is present. Magnetite occurs as 
fragments. 
The red part of the groundmass shows flow structure and is more 
cloudy than the gray part, owing to numerous little specks of ferrite. 
It is amorphous for the most part, with here and there specks of 
feldspar. The^ gray part appears to be impregnated with quartz. 
It contains elongated quartz-tilled cavities which grade into the more 
cloudy quartz-impregnated groundmass. In the center of some of 
the larger cavities there are brownish aggregates of fine cryptocrys- 
talline material. These silicious fillings are probably later than the 
rest of the rock, having been deposited in the porous parts. This 
