HV KEPORT OF THE STATE GEOLOGIST. 



down under those waters which, in their present restricted basin, we 

 call the Gulf of Mexico. 



The decided break between these formations and the older ones 

 which are found to the north and west, the difference in their dip and 

 the manner of their deposition, is sufficient warrant for the appropriate- 

 ness of the name of Gulf Border Formations for that part of the Ceno- 

 zoic group within the limits of this ancient shore line, which, as we now 

 know it, extended from Montague County, on Eed Kiver, to Travis 

 County, and thence west, along the Balcones, towards the Rio Grande. 

 The establishment of this shore line was the result of certain earth move- 

 ments which took place before and during the Lower Cretaceous Pe- 

 riod, and which were accompanied by volcanic disturbances, plain evi- 

 dences of which still remain in the hills of basaltic material scattered 

 from Austin to the Rio Grande, which marked its close. Pilot Knob, 

 nine miles south of Austin, is one of these ancient volcanoes, and there 

 are numerous others that could be mentioned. 



There is a strong probability that prior to this disturbance the area 

 which we have described as now occupied by these newer (Cenozoic) 

 deposits was an area of dry land, enclosing a great inland sea, which 

 stretched away, from what is now Burnet and Llano counties, to the 

 north and west, with possible connections with other similar waters in 

 those directions. 



The data at hand are insufficient to generalize too broadly on this at 

 present, but the entire character of the formations of what has been 

 designated the Central Palezoic Region, and which is the continuation 

 of the Central Basin of the United States, seems to demand the exist- 

 ence at times of just this shore line of a great land area to the south 

 and east, as a source from which such materials as we find in their 

 composition might be derived. 



THE CENTRAL BASIN FORMATIONS. 



Having then passed from the coast inward, until we have crossed 

 these descending series of the Cenozoic, we reach the Central Paleozoic 

 Area, with its nucleus of Archsean rocks, and here the usual order of 

 description can be best resumed, for as we pass on to the northwest 

 the various systems appear one after another in due chronological order. 



