136 H. P. BAIN — GEOLOGY OF THE WICHITA MOUNTAINS 



and collected in the same region. What is said here is based on macro- 

 scopic observation only. 



RAGGEDY MOUNTAIN GABBRO 



With the gabbro are classed here a considerable variety of dark basic 

 rocks, some of which, occurring in dikes, may prove to belong rather 

 with the diabases. The normal type is a dark noncrystalline rock show- 

 ing pyroxene and labradorite. West of Otter creek the rock shows fre- 

 quently great masses 6 to 8 inches across of pyroxene. Ilmenite is not 

 uncommon, and has been mistaken for tin ore. The gabbro areas are 

 characterized by low, almost flat surfaces (see plate 15, figure 1). The 

 rock apparently weathers down rapidly, and east of Mesquite valley 

 nowhere rises in sharp hills. It occurs along Medicine Bluff creek on 

 the north flank of mount Scott, where it is coarse grained and apparently 

 properly an anorthosite, and in the embayment between mount Sheridan 

 and Saddle mountain. It is found in limited areas north of Medicine 

 Bluff creek, rising from beneath the limestone. It was noted also in 

 what has been called the central valle}^ of the mountains, and is abund- 

 ant along the west flank of the mountains facing Mesquite valley. Low 

 knobs of this rock project through the floor of the valley, and near 

 the Upper Narrows it forms hills rising 500 feet along the creek. The 

 relations of the granite to the main gabbro mass is beyond dispute. 

 Northwest of mount Scott the granite was seen to cut the gabbro at 

 two points. Along the west flank of the mountains granite dikes run- 

 ning out into the gabbro are quite common. On Otter creek, about 

 half way between the Upper and Lower narrows a boss of granite rises 

 through a sheet of gabbro and sends out stringers into the latter on all 

 sides. Figure 2 of plate 15 represents a horizontal granite dike cutting 

 the gabbro of one of the high hills west of Otter creek. The presence 

 of a small stringer of granite running off from the dike and a sharp 

 covered block of gabbro imbedded in the granite is conclusive. 



The relations of the gabbro to the porphyry and associated rocks is 

 not so clear. In the Blue Creek canyon a gabbro area was noted wholly 

 within the porphyry and apparently under it. Near the same area a 

 dike of gabbro cuts the porphyry. The gabbro, as well as the porphyry, 

 has furnished material to the Cambrian basal conglomerates. Not all, 

 however, of these basic rocks belong with the main gabbro mass, since 

 in the Carrollton mountains a quartz vein cutting the porphyry is in 

 turn cut by a greenstone dike. 



CARROLLTON MOUNTAIN PORPHYRY 



There are two types or porphyry found in the region. The first has 

 a fine pink ground-mass, is set with phenocrysts of orthoclase and clear 



