FOSSILS, DIKES, FOLDS, FAULTS AND LAVA-FLOWS. 387 



18. Cardium afahann-ni^c, Gabb. = C. midtidrlafinn, Gabb. This spocics was also 



collected by Professor Cummins in 1889 across the Rio Grande river from 

 Presidio. 



19. CanJium tenu'u^triatinn, Whitfield (?) 



20. Ct/primeria, n. sp. (?) 



21. Liop'iKtha, sp. undet. Related to L. }>i'o(c.vl((, Con. 



22. Liopititha {Ci/mella), sp. undet. 



23. Pholadomi/a, sp. undet. Resembles P. rocmcri, AVhit. 



24. Teredo (?) tubes. 



25. An undescribed coral. 



Mr Stanton adds the following note : 



•* While the fauna as a whole is closely related to the Ripley (Navarro) fauna, 

 several of the species, and especially the ammonites, are not known to range so 

 high elsewhere. I regard the Eror/jp-a, the Placenticeras gnadalupx, and the two 

 species of Schloenbachia as especially important in determining the horizon as lower 

 than Ripley. The preponderance of evidence in the collection indicates that it 

 comes from a somewhat lower horizon lying somewhere between the Navarro beds 

 and the Austin limestone— that is, within the Ponderosa marls and probably 

 l)retty well down in them." 



A good specimen of the tooth of Plychodus mortoni., Ag., was also found. 



Dikes. — The valley is intersected by two series of dikes, one striking 

 north and south, the other and later east and west. They probably rep- 

 resent the fissures through which the two lava-flows of the mountain 

 welled up to the surface, although we found no immediate connection 

 between them. 



In one place where the coal seam is cut through by a dike the coal is 

 coked, but usually the metamorphism of the rocks along their courses 

 extends only a small distance on either side. 



Folds, Fmdls and Lava-flows. — Monoclinal folds are beautifully devel- 

 oped in this valley, with the same strike as the later dikes. The great 

 San Carlos fault, west of the camp, has a throw of over 2,300 feet, bring- 

 ing the upper lava-flow nearly to the level of the valley. The strike of 

 the fault is north and south and its downthrow is to the west. 



There seems to l>e an approximate synchronism between these lava- 

 flows and those of tlie Shumard knobs. The volcano of Pilot knol), 

 south of Austin, was active during the later stages of the Austin lime- 

 stone, and probably continued well into the Ponderosa, and since no 

 erosion was observed in tlie bed immediately underlying tlie first lava- 

 flow, this lava of the Viejo mountain is also seemingly of Ponderosa age. 



From the San Carlos and Balcones faults it is evident that the.se lines 

 of eruption continued to be lines of structural weakness long after the 

 dikes and lavas tbumsclves had cooled. Thus the main Balcones fault 



