DETAILED GEOLOGY 425 



indicate rapid subsidence of the region and relatively great distance from 

 a shore. 



Most remarkable exposures of Lower Cretaceous limestone form the 

 rim of the Solitario one mile in width on the north, east, and west sides, 

 dipping 30 degrees to 50 degrees (figure 3). More gentle dips on the 

 southeast extend these limestones 5 miles from the rim. The thickness 

 of the limestone must be over 3,000 feet. Above it and in the valleys 

 surrounding the rim the Del Rio clay and the Buda limestone may both 

 be recognized as at Del Eio. The latter is, in places, very white. 



Tapper Cretaceous sediments, except the Eagle Ford flags, are lacking. 

 These flags consist of bluish arenaceous shale and of sandstone, which 

 weather dark yellow in color. They compose the low hills on the outer 

 side of the circular drainage system and they also compose the low hills 

 south and southwest of the dome, where they become chalky. 



Lava flows and ash beds capping the volcanic plateau overlie the Eagle 

 Ford flags, but the folding in the latter is so gentle that the structural 

 relations with the flows were not observed. Elsewhere the Austin chalk 

 and Taylor marl or their equivalents have been found in western Texas, 

 but it is doubtful if they were ever deposited here. Uplift and volcanic 

 activity began after the Eagle Ford sedimentation. 



8TRVCTURE 



The structure of the Solitario is shown in the cross-sections presented 

 in figure 2. The Paleozoic rocks are closely compressed with folds, some 

 of which are isoclinal or even overturned. These folds are best seen in 

 the hills on the east and west — on the east where a creek cuts through 

 the novaculite and winds between two anticlines of novaculite, and on the 

 west in the novaculite ridges which finger out toward Burnt Camp into 

 anticlines which disappear beneath the Cretaceous. Another outcrop of 

 novaculite south of McGuirk's tanks is overlain by Cretaceous limestone. 



When the outcrops of novaculite are considered together, the contin- 

 uous aiul curved ridge on the east shows a pronounced dip outward from 

 the central plain ; the ridge on the south sliows tilting to the south and 

 the ridge on the west also shows a southern dip. On this evidence the 

 plain which forms the northern half of the uplift is believed to be anti- 

 clinorial, and the novaculite, which would normally outcrop in parts of 

 this area, is believed to have been eroded from an older arch in pre- 

 Cretaceous time. 



Subtracting the dips of the Cretaceous rocks from those of the Paleo- 



