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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 appropriateness of the name of Gulf Border Formations for that part of the Cenozoic group within the limits of this ancient shore line, which, as we now know it, extended from Montague County, on Red River, 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 movements which took place before and during the Lower Cretaceous Period, and which were accompanied by volcanic disturbances, plain evidences 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 existence 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 Archæan 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.