298 The American Geologist. November, 1903. 
Laccoliths. 
About six miles west and a little north of Fort Apache in 
the vicinity of the Kelley Butte region is a great mass of vol- 
canic rock, covering a half township, that has every indication 
of having been intrusive and laccolitic. It is, m structure, ex- 
actly like the volcanic rock in the body-wall of Kelley's butte. 
Moreover, the Carboniferous strata were domed by it origin- 
ally, as is attested by the tilted strata of that age now flanking 
it and overlying it on all sides. 
Since the volcanic epoch closed to which this laccolith be- 
longs, the agents of denudation have removed the overlying 
strata so that today its top and east flank are exposed. 
Extrusive Rocks, Volcanoes. 
Besides the numerous extinct volcanoes that are found 
along the dike-lines already mentioned, there are many cinder 
cones scattered here and there over the region, especially in the 
Xantan Plateau area. Most of these volcanoes are of the 
sanidin-doleryte type, the trachyte-rhyolyte craters, with few 
exceptions, being removed by erosion and covered over with 
Tertiary and Quaternary debris or with the lavas of later erup- 
tions. Some of these volcanoes are of the butte type and de- 
mand further mention. The remaining types will not be con- 
sidered further. 
Volcanic Buttcs. 
Among the volcanic buttes of the region are : Kelly. Sugar 
Loaf, Sanchez and Saw Tooth northwest of Fort Apache, and 
Chromo seventy miles southwest of Fort Apache. The former 
group are of the sanidin-doleryte type and penetrate Carbon- 
iferous strata, the latter is composed of trachyte (rhyolyte) 
and penetrates only Arcrjean schists at the surface. Both 
these groups protrude through the surrounding strata which 
are usually much broken and displaced. These buttes not only 
serve as an index of the amount of base-leveling that the coun- 
try has undergone since they were active, but, en account of 
the lavas and Quaternary and Tertiary sediments being re- 
moved from around them, they give opportunity to study the 
effect of intruded material upon the surrounding strata. Sugar 
Loaf, for example, not only reduced the surrounding sandstone 
to quartzytes and the lime rocks to marbles in its immediate 
vicinity; but the hot gases escaping from fissure vents at a con- 
