to earlier and later 'Formations. 433 



cing the Laramie into Mexico I had followed the trend of that 

 formation from the north, and thus passed to the westward of 

 the outcrops of the Gulf Tertiaries. 



In 1884, Professor E. D. Cope announced that he had found 

 " the Claiborne beds resting immediately upon the Laramie at 

 Laredo,"* Texas ; but he then mentioned no correlated facts 

 in support of this important announcement and, so far as I am 

 aware, none have since been published. The known south- 

 eastward trend of the Laramie, and the circling, and therefore 

 converging, trend of the Gulf series of formations made it evi- 

 dent that the district traversed by the lower "Rio Grande 

 would be found to be the most promising field in which to 

 search for the stratigraphical relation between the Laramie 

 and the Eocene Tertiary. With this object in view, I last 

 autumn visited that region and had the satisfaction of confirm- 

 ing the observation previously made by Professor Cope. 



Starting at Eagle Pass, Texas, I proceeded down upon the 

 Texan side of the valley of the Rio Grande to Laredo, mak- 

 ing observations by the way. The strata representing the Fox 

 Hills Group of the western section and the Ripley Group of 

 the eastern, were found to dip gradually in the direction of 

 the course of the river, and to receive those of the Laramie 

 Group upon them, the older strata passing finally from view 

 in that direction. 



The strata which are exposed in the bluffs along the left 

 bank of the Rio Grande from twenty-five to thirty miles above 

 Laredo, and which bear one or more workable beds of coal 

 there, are referred confidently to the Laramie, although they 

 afforded me only a few imperfect fossils. These strata dip 

 gradually to the southeastward or approximately in the direc- 

 tion of the river's course, and disappear beneath the sandy 

 strata of the Eocene Tertiary some ten or twelve miles above 

 Laredo. Below this, and all around Laredo, the strata which 

 I found exposed are of Eocene age ; and in many places they 

 bear an abundance of characteristic fossils. 



Going westward from Laredo to Lampazos in Mexico, I was 

 able to recognize the Eocene strata for a distance of about 

 twenty miles, beyond which the underlying rocks are so fully 

 obscured by the debris of the plain that no exposures were 

 observed until the neighborhood of Lampazos was reached. 

 The known presence of Laramie strata, a few miles to the 

 northward of Lampazos, which bear characteristic molluscan 

 fossils of that formation, however, leaves no room for doubt 

 that the Laramie is overlaid by the Eocene upon the Mexican 

 side of the Rio Grande, just as it is upon the Texan side. 



*Proc. Am. Philos. Soc, vol. xxi, p. 615. 



