76 



LARAMIE FLORA OF THE DENVER BASIN. 



horizon along the Rio Grande in adjacent 

 Texas. In a paper published in 1883 '° he 

 mentioned a small collection of invertebrates 

 obtainetl at a point about 7^ miles northwest 

 of Liimj)!izos, in the State of Nuevo Leon. He 

 oMumcrateil seven species, as follows: 



Ostrea wyomingensis Meek. 



Anomia microiipraa Meek. 



Miidiola regularis White? 



('orl)ula siibundifera White. 



Corbicula cytheriformis Meek and Ilayden? 



(jdontobasis buccinoides WTiite. 



Melania wyomingensis Meek. 



Concerning these invertebrates White said : 

 This Mexican collection, so far as it goes, is an almost 

 exact duplication of the Laramie molluscan fauna of the 

 Bitter Creek series as found at Rook Springs, Point of 

 Rocks, and Jilack lUittes, in southern Wyoming, points 

 which are more than a thou.saud miles north of the Me-x^ican 

 locality. 



The collection of invertebrates above listed 

 is not now known to be in existence, but 

 other similar material, collected later at or 

 near the same locality by White, is preserved 

 in the United States National Museum. I 

 am informed by T. W. Stanton, in whose 

 custody this material now is, that he does not 

 accept all these identifications as being cor- 

 rect, an<l further, certain of the species have 

 so great a known vertical range as to render 

 them of slight stratigraphic value. The com- 

 parisons that White made between the Mex- 

 ican specimens and the fauna of the "Bitter 

 Creek series" shows that at least two horizons 

 were tlien confused as Laramie. 



In 1888, in an article already mentioned, 

 Wiiitc" again referred to tliis Mexican locality, 

 writing as follows: 



Going westward from Laredo to Lampazos in Mexico 

 I wa.s able to recognize the Eocene .strata fur a distance of 

 al)out 20 miles, beyond which the underlying rocks are 

 so fully obscured by the debris of the plain that no ex- 

 posures were observeil until the neighljorhood of Lam- 

 pazos was reached. The known presence of Laramie 

 strata a few miles to the northward of Lampazos, which 

 bear characteristic moUuscau fos.sils 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. 



" White, C. A., Late observations concerning the molluscan fauna and 

 the geographical extent of the Laramie; Am. Jour. Sci., 3d ser., vol. 25, 

 pp. 207-209, 1H,S1. 



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

 later formations: Am. Jour. Sci., 3d ser., vol. 35, p. 433, 1888. 



This view was still entertained by White" 

 when he published his correlation essaj' in 

 1891, for we find him saying: 



The Laramie, which is such an important formation in 

 the two interior regions, is also an important one in the 

 north Mexican region, especially in the States of Chi- 

 huahua, Coahuila, and Nuevo Leon. Its prtjseiice in 

 the first-named State has just been mentioned, and it is 

 also well developed in the Sabinas Valley, in Coahuila, 

 where it is an important coal-bearing formation. 



It has also been recognized Ity its characteristic fossils 

 as far south as the vicinity of Lampazos, in the State of 

 Nuevo Leon. In this State, near to the Rio Grande, as 

 well as on the Texan side of that river, it has been found 

 to rest upon the equivalent of the Eagle Pass beds and in 

 tiu-n to pass by a gentle southerly dip beneath the marine 

 Eocene beds which occur there. 



The stratigraphic relation of the Laramie to the im- 

 mediately underlying Cretaceous formation is quite as 

 intimate in the north Mexican region as it is elsewhere. 

 The two formations appear to have been the result of con- 

 tinuous sedimentation, their interdelimitation being 

 marked only by a material change in the paleontologic 

 character of the strata. 



For a decade or more after the above- 

 recorded investigations by White compara- 

 tively little work bearing on the question under 

 consideration was done in northern Mexico. 

 As late as 1905, however, the Mexican geolo- 

 gists appear to have followed White in recog- 

 nizing the presence of Laramie. Thus Agui- 

 lera," in discussing the stratigraphy and struc- 

 ture of the State of Coahuila, accepted the 

 Laramie and described it as consisting of glau- 

 conitic sandstones with impressions of plants 

 and silicified wood. He placed it as equiva- 

 lent to the upper part of his Esperanzas beds 

 and above what has been called Eagle Pass 

 formation in the Texan section. 



E. T. Dumble has published sevend papers 

 on the geology of northern Mexico, though re- 

 lating mainly to the Tertiary part of the sec- 

 tion. Li one " he wrote of having traced the 

 Cretaceous-Tertiary contiict from Cabtdlero, on 

 the Kio Grande, to Kainones, 40 miles east of 

 Monterey. The uppermost Cretaceous strata 

 he referred to the Escondido formation. 



The conclusions reached concerning the pres- 

 ent disposition of the beds in western Texas 



^ White, C. A., Correlation papers — Cretaceous: U. S. Geol. Survey 

 Bull. 82, pp. 138 et soq., Isfll. 



" AguUera, J. G., Les giseinents carbouilires dc Coahuila: Cong. g(5oI. 

 mternat., 10' sess., Guide des excursions, Mexico, No. 27, pp. 1-17,1906 

 11907]. ^ 



" Dumble, E. T., Tertiary deposits of northca-sterlrtlexico: Science, 

 new ser., vol. 33, pp. 232-238, 1911. 



