LOWER CRETACEOUS. 597 



understand the structure of the locality and consequently counted the same sandstone twice as 

 two beds of different ages. At several points where the series of strata is clearly exposed and 

 but little disturbed we have been able to observe the true succession. In our excursion we fol- 

 lowed in part the road which Stanton and Vaughan followed, and we shall see what led to their 

 mistake. 



All of the sedimentary rocks with the exception of the recent conglomerate and sands belong 

 to the Cretaceous. Stanton and\ Vaughan recognized only their lower part, of which they give a 

 list of fossils, but their determinations differ in many cases from ours. With reference to this 

 subject we would refer the reader to our publications.'^ Stanton and Vaughan distinguished in 

 this lower part ten horizons which we are obliged to reduce to eight, but these horizons can not 

 be classed as real stratigraphic horizons. There are in fact in the lower part only two horizons, 

 to which we must also add two higher horizons which may be considered as such. We give a 

 summary of the distribution of fossils in the rocks. 



In his monograph on the Cerro de Muleros, which was not pubhshed until the 

 summer of 1910, Bose®^ says: 



According to my observations the succession .of the beds is as follows (from above down- 

 ward) : 

 No. 11. Brown sandstones alternating with argillaceous slate or shale, frequently containing Inoceramus lahiatus 



Schloth.; 110 meters. 

 No. 10. Whitish to yello'wish sandstone, highly quartzose and fine grained, with satiny argillaceous shale at the base, 



without fossils; 250 meters. 

 No. 9. White to clear gray limestone with Exogyra ponderosa: 10-20 meters. 

 No. 8. Yellowish marls with E. ponderosa, Hemisater calvini Clark, etc. ; 10-20 meters. 

 No. 7. Red, brown, and black sandstone in heavy beds, with E. ponderosa; 20-100 meters. 

 No. 6. Slate-colored brownish marls, sandstones, and limestones, with Ostrea quadripUcata; 10-20 meters. 

 No. 5. Gray marls with marly shales and beds of limestone with Schlcenbachia trinodosa; 30-50 meters. 

 No. 4. Argillaceous shales, marls, and beds of limestone, with Schlcenbachia nodosa; 30-50 meters. 

 No. 3. Gray limestones in thiu-bedded calcareous gray sandstones and brown to yellow marls and black argillaceous 



shales, with Schlcenbachia cfr. helknapi; 10 meters. 

 No. 2. Brown marls with beds of limestone and calcareous sandstone with Schlcenbachia bravoensis; 10-20 meters. 

 No. 1. Hard limestones in thick beds and of a gray color, with Turritella vibrayeana; 20-25 meters. 



Our subdivisions 1 to 7 correspond to the horizons which were numbered 1 to 7 by Stanton 

 and Vaughan, 8 and 9 to the horizons 9 and 8 of those authors, since in fact the limestones 

 with E. ponderosa are above the marls which carry the same fossU. That which Stanton and 

 Vaughan regarded as their horizon No. 10 is in reality the same sandstone as their horizon 

 No. 7, and the two American authors did not see our subdivisions 10 and 11. We shall see in 

 the discussion of the structure why they mistook a recumbent synchnal for a normal succession. 

 If they had gone on to the porphyry they probably would not have fallen into this error, since 

 one may there see clearly that the beds or the strata with Ostrea quadripUcata rest on the 

 sandstone No. 7 of our classification, which is the horizon No. 10 of Stanton and Vaughan. 



Richardson ^^^^ studied the occurrences of the Cretaceous near El Paso north of 

 the Rio Grande and made some subdivisions. He says: 



The Cretaceous system is represented here by the Fredericksburg and Washita groups 

 of the Comanche series. The Trinity group has not been recognized in this area, nor has the 

 Upper Cretaceous been found (with the possible exception that a few small areas of shale in the 

 city of El Paso are of Upper Cretaceous age), though rocks belonging to both of these' ages 

 occur not far to the south and west. 



The Fredericksburg is separated into three formations — the Campagrande, the Cox, and 

 the Finlay, which are differentiated by their lithologic features. AH these contain Fredericks- 



o Bose, Emil, Monograffa geol6gica y paleontol6gica del Cerro de Muleros, cerca de Ciudad Juarez, Chih.: Bol. del 

 Inst. Geol. de Mexico, No. 25. 



