594 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



The massive limestones underlie these sands and clays, and, as far as could be seen, without 

 any unconf ormability. These limestones seem to correspond very well with Aguilera's description 

 of the Middle Cretaceous. The Gryphsea which they carry in such abundance resembles very 

 closely the variety found at the base of the Fredericksburg beds, in northern Coahuila. 



H 13. QUITMAN MOUNTAINS, TBANS-PECOS TEXAS. 



The Quitman Range crosses the thirty-first parallel near longitude 105° 25' 

 and extends northward to Malone Mountain and southward to the Rio Grande. 

 The development of the Comanche series in the southern portion of the range is thus 

 described by Stanton"^* in Cragin's report on Malone Mountain: 



Cretaceous rocks have a great development in this region and represent the three main 

 divisions of the Comanche series — the Trinity, Fredericksburg, and Washita — as well as a part 

 of the Upper Cretaceous. Lithologically the section differs greatly from that of central Texas, 

 where the Comanche series has been most studied, and there are also considerable differences 

 in the vertical range of some of the common species, so that it is impracticable to recognize 

 many of the minor formations and horizons that have been studied. The general faunal suc- 

 cession is the same in both regions, and it is usually not difficult to classify the beds by means 

 of the fossils as Trinity, Fredericksburg, or Washita, though it was difficult and sometimes 

 impossible to assign each exposure to its exact position in the general section, because many 

 of them are relatively small and isolated and the structure is complicated by folds, faults, and 

 igneous iatrusions. The most complete sections are to be found in the Quitman Mountains, 

 especially toward the southern end and in the lower hills farther south on the Rio Grande, ia 

 the southern extension of the same line of uplift. 



The description of the Quitman Range comprises notes on structure and on 

 igneous intrusions, as well as on stratigraphy, and the more complete section near 

 the Rio Grande is given as follows : 



Still farther south, near the Rio Grande, the upper part of the section is much more com- 

 plete and more simple, furnishing the key to the sections already discussed, which are parallel 

 with it across the same line of uplift. The eastern end of the section is about 1 mile north of 

 the Rio Grande in the first hills west of the broad valley of Quitman Arroyo. Here the beds 

 are sharply folded and a prominent ridge shows an anticline consisting of argillaceous limestone 

 belonging to the Waslxita division. 



The western limb of the anticline dips 70° to 80° W., and the exposure is as follows: 



Section in JiiUs just west of Quitman Arroyo, about 1 mile north of tTie Rio Grande. 



Feet. 



1. Argillaceous limestone, weathering in nodular form, with bands of harder limestone 200 



2. More massive limestone, much seamed and fissured 30 



3. Dark, fissile shale, with occasional bands of impure brown limestone, underlying a valley 



about 1 mile wide. Dips at first steep to the west, becoming variable and much less 

 toward the middle of the valley and again steep to the west on the west side of the valley. 

 Inoceramus labiatus and a few other Upper Cretaceous fossils were found west of the middle 

 of the valley; thickness apparently several thousand feet. 



4. Massive limestone, probably same as No. 2 30 



5. Argillaceous limestone with some bands of olay and sandstone; fossils: Nodosaria texana, 



Enallaster texanus, Neiihea texana, Exogyra arietina, E. draJcei var., Plicatula incongrua, 



and other Washita forms 300 



6. Heavy-bedded limestone (40 feet) forming a clifi, followed by argillaceous nodular limestone 



(30 feet), which yielded Enallaster texanus, Gryphxa comigata. Limn wacoensis, Neiihea 

 texana, and Schloenbachia vespertina 70 



7. Similar limestones with dip not less than 45° westward 300 



