THE BOSQUE AND FREDERICKSBURG DIVISIONS. o7\) 



Exposures III the Arlwlcs and Boras Mountains. — In the Arboles and 

 Biirras nionntains I found only the Alternating beds, which have tliere 

 a very consideral)le thickness, and closely resemble the beds in the Colo- 

 rado section, both in the character of the rocks and in the fossils, inchid- 

 ing the beds of Re<iuienia icxana, Roenier. 



I did not find that these Glen Rose beds cut through at any ])oint in 

 the mountains visited, but, in all probability, the Trinity sands will be 

 found underlying them, being indicated by the occurrence of springs in 

 the various canyons. 



Episodes of the Bosque Period. — In the Bosque period, therefore, the con- 

 ditions seem to have been the same over the entire Texan area. The 

 encroachment of the sea was from the south over a gradually subsiding 

 sea-bottom. The advancing shoreline is marked by the deposits of 

 Trinity sands accompanied and followed, in the deepening waters, b}'' 

 the Glen Rose beds, which, while of considerable thickness toward the 

 south, decrease and finally wedge out toward the north, passing imj^er- 

 ceptibly into the Paluxv sands, which are the latest deposits of the i)e- 

 riod, and, with the thin bedded marl}^ limestones of the south, mark the 

 shallowing waters of its close. 



FREDERICKSB URG DI VISION. 



West of the Pecos River. — West of the Pecos river the Fredericksburg 

 division has its most meager development along the Texas and Pacific 

 railroad. At Kent it is not more than 50 feet in thickness, and in the 

 vicinity of Sierra Blanca it is only 40 feet thick. Generally the Comanche 

 Peak beds are missing, and the Caprina limestone rests immediately on 

 the Exogyra texana bed.* 



In the San Lorenzo Section. — In the Arboles mountains there is no ap- 

 parent break in the sedimentation between the Glen Rose beds and the 

 ExMciyra texana, and the onlv means of determining where the one ends 

 and tlie other begins is by the (lisapi)earance of the comjjarati vely smooth 

 and small form of the PJxnf/i/ra of the former and the ap])earance of the 

 better known E. texana^ which gives its name to the latter. 



The Exorpjra trxana beds and the overlying Comanche Peak ])eds present 

 little or no variation in the San Lorenzo section from their normal char- 

 acter. The Caj)rina limestone, howevei', has an extraordinary thickness 

 and presents some differences in the distril)Ution of the fossils. The 

 limestones of tliis stage are massive and cherty, as usual, ])Ut the Caprina 

 crnssijibra, wliich at all otiier localities examined ap})ears in continuous 

 bands, occurs here in nests and at several different horizons. Between 

 horizons of the Caprina limestone, in the lower i)art of the beds, are l)an(ls 



* For details see Second Ann. Rep. Geol. Survey of Texas, p. 717. 



