HISTORICAL REVIEW OF THE LARAMIE PROBLEM. 



75 



Ijeen oljserved there only in the valley of the Rio Grande 

 and in that of the Xueces River, Imt there seems to be lit- 

 tle room for doubt that the lignite beds of eastern Texas, 

 as well as those of the State of Mississippi, which are 

 usually regarded as of early Eocene age, are really equiva- 

 lent to the upper part of the Laramie. 



The presence of the Laramie formation in 

 western Texas, so confidently proclaimed by 

 White, has not been confirmed by subsequent 

 workers in this field; in fact, in the year fol- 

 lowing the pul)lication of his paper above 

 mentioned, Penrose"^ in a way laid the foun- 

 dation for a quite different interpretation of 

 the section. In speaking of the Cretaceous 

 along the Rio Grande he said : 



It may be said, however, that Cretaceous fossils have 

 been found at Eagle Pass, and from there down the river 

 to the Webb County line are found great iiuantities of am- 

 monites and other fauna of that epoch. In fact, it is not 

 until we reach a point 3 miles below the northwest corner 

 of Webb County that true Tertiary (^or Laramie) forms are 

 found. 



In 1892 Durable "" studied this same section, 

 concerning which he wrote as follows: 



From this point [10 miles below Eagle Pass] to the falls 

 of the Rio Grande, just above the Webb County line, the 

 exposures are but repetitions one of another — brown, buff, 

 blue, or green clays, with sandstones, .sometimes friable 

 and sometimes so indurated as to be semiquartzites. 

 Abundant fossils, consiting of ammonites (Placenticeras), 

 oysters, and gastropods, are found. The rapids (or falls of 

 the Rio Grandej, which continue almost to the line be- 

 tween the two counties, are formed l>y the edges of some of 

 these ammonite-bearing beds as they pass below water 

 level. From this point to the Weblj Bluff, a distance of 3 

 miles, no fossils were found; but there was no change in 

 the lithologic character of the rock materials, nor could 

 the clays at the ba.se of the Webb Bluff section be distin- 

 guished in any way from those observed at the rapids 

 alcove. * * * We have, therefore, only 3 miles in 

 which there can be any room for deposits intermediate be- 

 tween strata containing fossils of recognized and decisively 

 Cretaceous forms and those containing marine Eocene 

 forms. The average dip does not exceed 100 feet per 

 mile, and we saw nothing in any of the exposures on 

 either bank of the river in this space to indicate a change 

 until we reached Webl) Bluff itself. 



In 1900 Vaughan,'*' in a paper entitled "Re- 

 connaissance in the Rio Grande coal fields of 

 Texas," discussed the Cretaceous-Eocene con- 

 tact along the Rio Grande. He agreed with 

 White, Penrose, and Dumble that there is no 

 sharp hthologic line between the Cretaceous 



<• Penrose, R. A. F.. jr., Texas Geol. Survey First Ann. Rept., pp 

 .•iS-ll, 1S89. 

 M Dumble, E. T., Geol. .Soc. America Bull., vol. 3, pp. 228, 229, 1892. 

 «' Vaughan, T. \V., L". S. Geol. Survey Bull. 160, i)p. 35 et seq., 1900. 



and Eocene; in fact, no actual contact had 

 been discovered up to that time. \'aughan 

 added : 



The principal result of the writers work on the Rio 

 Grande was in proving the existence of Eocene fossils 

 some 3 or 4 miles above the Webb-Maverick county line, 

 6 or 7 miles above where Penrose and Dumble first found 

 such fossils. The fossils olitained here are typical lower 

 Eocene. 



In 1911 Durable "' published additional re- 

 marks on the Cretaceous-Eocene contact along 

 the Rio Grande, in which he stated that tlie 

 contact is "well shown below Toro Colorado, 

 just above the falls of the Rio Grande and on 

 Caballero Creek." 



In the fall of 1912 L. W. Stephenson "^ made 

 investigations in Maverick County, Tex., which, 

 he said, " resulted in the exact determination of 

 the Cretaceous-Eocene contact along the river 

 [Rio Grande] and the approximate determina- 

 tion of the outcrop of the contact northward 

 through the county." He found the contact at 

 a point on the Rio Grande below White Bluff, 

 about 5 miles above the Webb County line. At 

 this point the undoubted Upper Cretaceous 

 beds, known as the Escondido formation, are 

 overlain unconformably by undoubtetl marine 

 Eocene, the contact between thera being sharp 

 and slightly undulating. 



The results above set forth appear to settle 

 conclusively the fate of the Laramie of western 

 Texas as advocated by WHiite. The highest 

 Cretaceous beds of the region are known as the 

 Escondido formation and correspond approxi- 

 raately to the Fox Hills of the Rocky Moun- 

 tain area and the Ripley formation of the Gulf 

 coast. Above the Escondido formation are 

 the beds referred by White to the Laramie, but 

 all recent workers in the field agree that they 

 are undoubtedly Eocene. The lowest is the 

 Midway formation, above which is the Wilcox 

 formation, which in turn is overlain, at least in 

 certain areas, by the Claiborne or upper Eocene. 



NORTHERN MEXICO. 



So far as I know C. A. White was the first to 

 announce that the Laramie is present in north- 

 ern Mexico, a conclusion whicli of course fol- 

 lowed from his supposed identification of this 



» Dumble, E. T., Rediscovery of some Conrad forms: Science, newser., 

 vol.33, p. 971, 1911. 



«3 Stephenson, L. W., The Cretaceous-Eocene contact in the Atlantic 

 and Gulf Coastal Plain: U. S. Geol. Survey Prof. Paper 90, pp. 155-182, 

 1915. 



