112 EXPLORING EXrEDITIOX FEOM SANTA KG 



before mentioned. A sage-plain with rolling surface, fashioned by erosion, on which 



rise the extreme Upper Cretaceous (?) strata in buttes and detached mesas." 

 One of these buttes at Camp 48 afforded me the following section : 



Feet. 



1. Soft yellow sandstone 60 



2. Greenish-white marl 70 



3. Soft yellow sandstone with large concretions, weathering brown. 50 



1. .Marl, greenish- white above, purple below 75 



5. Soft white sandstone with hard concretions 20 



6. Marls, greenish-white above, purple below, with concretions of silicious lime- 



stone-- 50 



7. Coarse, soft, whitish sandstone 30 



8. Greenish-white and purple marls 90 



This series should be added to that of the cliff at Camp 46. 



Just before reaching the base of the Nacimiento Mountain, we crossed the divide 

 between the Pacific and Atlantic, and reached the highest point, geologically, attained 

 on any part of our route. The immediate base of the mountain is swept by a line of 

 drainage which flows south along its western side, around its southern extremitA' 

 passes into the Pnerco, and thence into the Rio Grande. The line of divide diverges 

 from the north end of the Nacimiento Mountain, running southwesterly to San Mateo 

 and the Sierra Madre. For at least a hundred miles it stretches across the table-lands 

 unmarked by any disruption of the strata or line of upheaval. 



The crest of the water-shed is here formed of series of buttes and mesas com- 

 posed of soft, marly strata: the extreme summit of the great group, which, on nega- 

 tive rather than positive evidence, I have designated as Upper Cretaceous. 



BUTTES WEST OF THE NACimEXTO MOUNTAIN (EOCEXE TERTIARY (.'). 



These buttes include about 400 feet of strata not included in the sections before 

 given. They are as follows : 



Feet. 



1. Soft yellow sandstone 40 



2. Purple, yellow, and greenish soft marls GO 



3. Soft yellow sandstone 35 



4. Green, purple, yellow, and white marls, with thin layers of white sandstone. . 70 



5. White sandstone 25 



6. Green and purple- marls 80 



7. Coarse, white sandstone 20 



8. White and purple marls 50 



9. Soft yellow sandstone, summit of cliff in section at Camp 48. 



These strata are all conformable among themselves and to those below ; lying 

 nearly or quite horizontal. The marls of this series are darker than those of the preceding 

 sections, having a purplish-green appearance at a distance. . The sandstones are very 

 soft, and being thinner than the mails they form but a slight interruption to the uni- 

 formity of the slope of the sides of the buttes, and are scarcely noticeable, except 



