74 



LARAMIE FLORA OF THE DENVER. BASIN. 



formation. Nothing like this has been noted in the 

 underlying beds, and to a certain extent it argues for the 

 Tertiary age of the Ojo Alamo beds, though obviously 

 the evidence is not strong. For the present, therefore, the 

 dictum based on the evidence of the fossil vertebrates that 

 these beds can not be separated from the underlying beds 

 must be accepted, though the writer can not escape the 

 impression that they may ultimately be shown to be of 

 Tertiary age. 



From till' above exposition it appears that 

 the plants and vertebrates are in substantial 

 agreement in indicating a Montana age (Mesa- 

 verde or .Iiidith River position) for the beds 

 previously considered referable to the Laramie, 

 whereas the invertebrates are interpreted as 

 "indicating an epoch considerably later than 

 Mesaverde and Judith River and possibly 

 somewhat earlier titan Lance." 



•LARAMIE" IN WESTERN TEXAS AND NORTHERN 

 MEXICO. 



WESTERN TEXAS. 



The extreme desirability of establishing a 

 connection between the late Cretaceous and 

 early Tertiary section of the great interior 

 region and the well-authenticated marine sec- 

 tion cff the Gulf coast region has long been 

 recognizetl. The Laramie in particular was 

 one of the stratigraphic units characteristic of 

 the Rocky Mountain region that it was hoped 

 might sometime be brought into harmony with 

 the marine succession of the Coastal Plain. 

 C. A. White, who had taken so large a part in 

 the exploitation of the Laramie and who was 

 more or less familiar with both these areas, was 

 especially desirous of establishing such a rela- 

 tion. Ill an article published in 1888 "- he says: 



During the 12 years preceding the autumn of 1887, in 

 wliich I had made extensive studies and observations con. 

 corning th(^ Laramie group, 1 was never able to obtain any 

 pcr.sjiial knowled.ge of the actual .flratigraphic relation of 

 that group to any of the marine Tertiary groups which 

 border various portions (jf Norlh .\merica. 



He then wrote of having studied the Laramie 

 from the State of Nuevo Leon, Mexico, on the 

 south, to northern Montana on the north, and 

 added that within this vast region 



wherever any strata were found resting upon the Laramie 

 they were always those of the great fresh-water Tertiary 

 series; but 1 had not then traced the Laramie into a distric't 

 witliin which marine Tertiary strata were known to exist. 

 That is, in tracing the Laramie into Mexico I had followed 



" White.C. A., On the relation of the Laramie group to earlier and later 

 formations: Am. Jour. Scl., 3d ser., vol. 3.% pp. 4.32-438, 1888. 



the trend of that formation from the north and thus 

 passed to the westward of the outcrops of the Gulf 

 Tertiaries. 



In 1884 Prof. E. D. Cope " announced that he had 

 found "the Claiborne beds resting immediately upon the 

 Laramie at Laredo," Tex., but he then mentioned no 

 correlated facta in support of this important announce- 

 ment, and, so far as I am aware, none have since been 

 published. The known southeastward trend of the Lar- 

 amie and the circling and therefore converging trend of the 

 Gulf series of formations made it evident that the district 

 traversed by the lower Rio Grande would be found to be 

 the most promising field in which to search for the strati- 

 graphical relation between the Laramie and the Eocene 

 Tertiary. With this object in view, I last autumn visited 

 that region and had the satisfaction of confirming the 

 observation pre\'iously made by Prof. Cope. 



Starting at Eagle Pass, Tex., I proceeded down upon 

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

 making 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 25 to 30 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 direction of the river's course, and disappear be- 

 neath the sandy strata of the Eocene Tertiary some 10 

 or 12 miles above Laredo. Below this and all around 

 Laredo the strata which I found exposed sire of Eocene 

 age, and in many places they bear an abundance of 

 characteristic fossils. 



While I have no doubt as to the Laramie age of the 

 strata referred to, which I observed on both sides of the 

 Rio Grande, and none as to the Eocene age of the strata 

 which I found overlying them, I am by no means certain 

 that the lowermost strata which I found resting upon 

 the Laramie near Laredo represent the lowermost strata 

 of the Eocene division of the Gulf series. Indeed, so 

 fiir as I could discover, no equivalent of the "Northern 

 Lignite," the lowermost member of (he Eocene of IIil,s;ard's 

 Mississipiii section, exists in the region round al)OUt 

 Laredo, unless the coal-bearing strata of the upper poilion 

 of the Laramie are really its equivalent. I am disposed 

 to accept this view of the case and to regard the Northern 

 Lignite of the Mississippi section and its equivalent 

 elsewhere, including the uppermost strata of the Laramie, 

 as really of Eocene age. 



The view above expressed was entertained 

 by White when he published his correlation 

 paper on the Cretaceous in 189L"^ He said: 



The Laramie formation prevails over a large part of the 

 Great Interior area, but within the Texas region it has 

 been recognized only in western Texas, and it has hitherto 



"Cope, K. D., .\m. I'hilos. Soc. Proc., vol. 3, p. 615, 1S84. 

 " White, C. A., U. S. Geol. Survey Bull. 82, p. 117, 1891. 



