554 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Burckhardt's description"" is as follows: 



The Jurassic and Cretaceous series of the Sierra de Mazapil is composed of four great natural 

 subdivisions. At the base one may observe heavy-bedded hmestones which attain great thick- 

 ness and are the hmestones with Nerinea. These are the Upper Jurassic limestones which form 

 the center of the antichnes of the two ranges and which, since each chain is composed of a single 

 anticline, occupy generally the highest portions, the peaks and crests of the sierras. 



The flanks of the two chains are also formed by heavy masses of hmestone of great thickness 

 which locally resemble the limestones with Nerinea, but which, even so, may be readily dis- 

 tinguished by their petrographic character. These hmestones are generally weU stratified and 

 contain a great deal of chert in beds and lenses which alternate with them. The fossil fauna 

 of these hmestones indicates that they correspond to different divisions of the Lower and 

 Middle Cretaceous. 



Between the two masses of hmestones which have been described there occurs a zone of 

 less compact strata composed of clays, marls, and slates, with intercalations of hmestone. 

 * * * The colors of these rocks are generaUy dark and contrast strikingly with the clear colors 

 of the hmestone masses between which they occur. The beds are very fossiliferous and have 

 furnished a large number of weU-preserved specimens, which demonstrate that they belong to 

 the Kimeridge and Portland. 



The latest stratigraphic division which may be observed in the region, in the valleys and 

 at the foot of the sierras, covers the Cretaceous limestones that have been cited. It consists 

 of shales, in part sandy and in part argillaceous, of which the lower portion, the shales with 

 Inoceramus, belongs to the Upper Cretaceous (Lower Turonian). 



H 13. TEXAS. 



In southwestern Texas, just north of latitude 31°, near the line of the Southern 

 Pacific Railroad, Malone Mountain rises from the desert plains north of the Quitman 

 Mountains and is formed in large part of Jurassic strata. The fauna was discovered 

 and described by Cragin,^^^ and the general geology of the region has been stated by 

 Stanton in a brief chapter in Cragin's report, which contains also a detailed section. 

 Stanton says: 



The most complete section that I observed, in which the thicknesses were estimated with 

 some care, extends across the mountain from a point on the east side about one-half mile south 

 of Malone station. The eastern face of the mountain shows an apparent thickness of about 

 1,200 feet of blue and gray limestones, with a few intercalated beds and bands of conglomerate 

 and sandstone, the beds all dipping strongly westward with increasing dips until they become 

 vertical on the crest. On the west slope there is a succession of limestones, conglomerates, and 

 gypsum beds, nearly vertical, and not weU exposed, and farther down these are apparently 

 repeated with a westerly dip, overlain by conglomerates, hmestones, etc.; fairly well exposed and 

 not much disturbed in the lower ridges to the west. The gypsum beds and the hmestones imme- 

 diately associated with them appear to be the oldest rocks exposed. 



I-K 10-11. COAST RANGE, CALIFORNIA. 



The Franciscan formation of the Coast Range of California is regarded by 

 Lawson as of Cretaceous age but is generally placed in the Jurassic. The basis for 

 Lawson's view is the relation of the Franciscan formation to the Montara granite, 

 which is one of stratigraphic unconformity. Lawson correlates the granite tenta- 

 tively with the late Jurassic granite of the Sierra Nevada and infers accordingly that 

 the sedimentary Franciscan formation, which rests unconformabl} upon the granite, 



