484 G. B. Iii chard. son — Paleozoic Formations. 



(Hueco) limestone lies with apparent conformity on Silurian 

 (Fusselman) limestone. The absence of the intermediate 

 series between the Cambrian and Pennsylvania!! in the two 

 quadrangles points to several uplifts which in general did not 

 appreciably deform the rocks, and apparently the emergences 

 were so slight that there is little record of erosion. But in 

 the Yan Horn region there is abundant evidence of pro- 

 found pre-Penn sylvan ian erosion, for the Hueco limestone 

 with a well-developed basal conglomerate rests indifferently on 

 all of the underlying formations. The deposition of the sand- 

 stone members of the Guadalupian series indicates changed con- 

 ditions during late Paleozoic time in contrast to those prevailing 

 during the accumulation of the great mass of limestone in the 

 earlier periods, but the extent and relationships of these 

 Permian ? strata have not yet been determined. 



The close of the Paleozoic era in the trans-Pecos Texas 

 region apparently was accompanied by general uplift, but there 

 is little record of immediately succeeding events. Early 

 Mesozoic rocks are known in only a few areas, such as the 

 marine Jurassic beds in the Malone Mountains,* 65 miles 

 southeast of El Paso. East of the Yan Horn quadrangle 

 the Delaware Mountain formation is unconformably overlain 

 by several hundred feet of gypsum of undetermined age. 

 There is abundant evidence of considerable post-Carboniferous, 

 pre-Cretaceous erosion in this region and in several places the 

 Hueco limestone is immediately overlain by Lower Cretaceous 

 strata. 



U. S. Geological Survey, Washington, D. C. 



* Bulletin No. 266, U. S. Geological Survey, 1905. 



