444 C. A. White — Lower Cretaceous of the Southwest. 



One of these short ranges lying in the Mexican state of 

 Chihuahua, 75 miles southeastward from Presidio del Norte, 

 and known as the Sierra San Carlos, was observed by Dr. New- 

 berry several years ago, and lately by myself, to consist mainly 

 of the hard bluish limestones which, from bottom to top carry 

 fossil forms which are characteristic of the Comanche series. 

 These strata which are there strongly upturned and flexed, have 

 a thickness of fully 4,000 feet, to which should probably be 

 added 500 feet of similar and conformable strata at the base of 

 the former, the only doubt as to their being a part of the 

 Lower Cretaceous series there arising from the obliteration or 

 obscuration of the contained fossils. These latter strata which, 

 it may be incidently mentioned, contain deposits of argentif- 

 erous galena, rest with apparent conformity upon others which 

 are mostly siliceous, highly metamorphosed, and probably of 

 pre-Silurian age. The latter in turn rest upon the crystalline 

 granitic rock which has already been referred to, and which 

 seems to form the core of the mountain range. 



At the eastern base of the range about 700 feet in thickness 

 of strata occur which bear Inoceramus proMematicus and 

 other Upper Cretaceous fossils. The lowermost of these Upper 

 Cretaceous strata are there almost vertical, and they are appar- 

 ently conformable with the almost vertical Lower Cretaceous 

 strata with which they are in contact ; so that it is evident that 

 both the Upper and Lower Cretaceous were involved in one 

 and the same displacement. Because of this apparent con- 

 formity the stratigraphical hiatus which is understood to exist 

 between the Upper and Lower Cretaceous is not distinctly 

 shown here. 



There is no apparent reason for supposing that the much 

 altered strata which underlie the Lower Cretaceous in the San 

 Carlos Mountains are of Mesozoic age, and therefore it is 

 assumed that both the Jura and Trias, perhaps also the Carbon- 

 iferous, Devonian and Silurain are absent there. It is such 

 evidence as this of a great hiatus beneath the Lower Cretace- 

 ous that has been referred to. 



The only other uplift of Lower Cretaceous strata that will 

 be specially mentioned in this article occurs in the Chinate 

 Mountains, in Texas, about 25 miles north of Presidio del 

 Norte. At the eastern end of this range, near the Shatter 

 silver mines, the Lower Cretaceous* strata are found resting 

 directly and conformably upon the Carboniferous limestones ; 

 both formations being composed of limestones which are so 

 similar in color and lithological character that their difference 

 in age would hardly be suspected by casual observation, and is 

 only demonstrable by the discovery of characteristic fossils in 



* These Cretaceous strata also bear silver ores. 



