AGE OF THE GLEN ROSE BEDS. 



509 



beds are surmounted by the Walnut clays, or Exogyra texana beds, which I 

 assume in this paper to be the base of the true Cretaceous. North of the 

 Lampasas they are overlain by the Paluxy sands, an arenaceous terrane 

 hitherto unrecognized and undifferentiated from the Trinity division. 



There are in these beds many layers of dimension stone of almost identical 

 lithologic character with that of the celebrated Caen quarries of France, so 

 largely imported into our northern seaports. This stone is extensively quar- 

 ried at Weatherford, Granbury, Belton, Oatmanville, Kerrville and other 

 places, and will no doubt some day occupy an important position in the 

 resources of our country. 



The Thorp Springs limestone subdivision, found near the base of the 

 alternating beds and overlying the Trinity sands, is o)}e of the Caprotina 

 limestones of Shuraard. It is a massive stratum, composed almost exclu- 

 sively of shells of the peculiar Requienia (Caprotina) texana, Roemer; a fossil 

 not confined exclusively, however, to this bed. In thickness it is about 

 twenty feet. It outcrops for many miles along the bed of the river at Gran- 

 bury and Thorp Springs, and also in the bed of the Paluxy at Glen Rose. 

 Near Travis Peak post-office, on the Colorado, this horizon is again seen, and 

 is apparently persistent. Owing to the excessive faulting in the vicinity of 

 Austin, it is impossible to say what relation this stone bears to the Caprotina 

 limestone west of that city. 



The different lithologic and stratigraphic features of the Glen Rose alter- 

 nating beds, their position beneath the Fredericksburg division (separated in 

 the north by a sandy, littoral terrane), and the entire absence of the great 

 characteristic fauna of the hitherto recognized Fredericksburg division, en- 

 title these beds to a distinct position, although they are separated by no struc- 

 tural unconformity. I cannot here enter into a discussion of paleontologic 

 details, but I consider the deposits of Jurassic rather than of Cretaceous affini- 

 ties. The question of age is secondary to definition, however, and I shall 

 leave this to a future time. The fossils have not yet been studied critically; 

 but I have in my possession a representative series of these fossils, which I 

 propose to make the subject of a separate paper at an early day. 



THE FREDERICKSBURG OR COMANCHE PEAK DIVISION. 



General Composition. — This is the second of the great divisions of the 

 Comanche series, and is distinguished from the others by its more chalky 

 character and its unique molluscan fauna. The Paluxy sands are placed 

 with this series only tentatively, for there are some few reasons which might 

 be sufficient to class them with the Trinity division. The rocks of this 

 division, although of wide extent, have their characteristic exposure and 

 development in the region of Texas west of the meridian 97° 30', and be- 

 tween the Trinity and Lampasas rivers. 



