72 EXPLORING EXPEDITION FEOM SANTA Ffi 



Foot. 



4. Black shales with bands of light-dove-colorcd limestone 150 



The upper of these shale-beds is greenish-brown, with bands of foliated 

 sandy limestone, containing immense numbers of fragmentary or entire 

 fossils. These are principally Inoceramus problcmaticus, J. fray/Us, Ostrcn 

 congcsta, J3aculitcs anccps, Scapliites Warrcni, 8. laviformis, <&c. 



5. Bluish-black shales, with concretions and bands of limestone containing a 



large undulated Inoceramus, the broken fragments of which are thickly 



set with Ostrca congesta 1 , 000 



The lithological characters of this division are nearly the same through- 

 out, but the limestone bands and fossils are nearly restricted to the lower 

 portion. The layers of limestone are from 6 to 12 inches in thickness, 

 quite pure and compact, blue in color, but weathering reddish yellow, 

 and breaking on exposure in vertical prisms, like starch. 

 H. A light dove-colored sandy limestone or calcareous sandstone, weathering 



yellow, massive toward the top, foliated below, without fossils 200 



7. This, the cap-rock of the high mesa, is a higher member of the Cretaceous 



series than has before been met with in New Mexico. Our subsequent 

 observations showed it to be the base of the third great division of this 

 formation as developed on the Colorado Plateau. 



8. Gravel hills, valley drift. 



At the Laguna de los Cavallos we reached the summit of the divide between the 

 waters of the Pacific and the Atlantic, at the height of 7,600 feet. No conspicuous 

 elevation marks the summit, but the strata are somewhat broken by a line of displace- 

 ment, apparently a continuation of the Nacimiento axis. The country about the 

 Laguna may be taken as a type, both as regards its general aspects and its geological 

 structure, of all that bordering our route while we were skirting the bases of the 

 mountain ranges, the drainage of which supplies the flow of the San Juan River and 

 its tributaries. This region includes three topographical belts or districts in which the 

 physical features exhibit the most striking contrasts, viz., the mountains, the foot-hill.*, 

 and the table-lands. The mountainous district includes a large number of lofty 

 chains, having a north and south trend and the general characteristics of the Rocky 

 Mountain system, connected by thousands of interlocking spurs, or separated by nar- 

 row valleys, traversed by clear, cold, and rapid streams. These ranges terminate 

 southward en echelon, and, when viewed from a distance, present the appearance of 

 a continuous sierra, having a northwest and southeast trend. The oxitlines of these 

 mountains are bold and picturesque ; their highest summits having an altitude of 

 12,000 or 13,000 feet, entirely bare of vegetation, and showing, here and there, 

 patches of perpetual snow; their slopes covered with forests of spruce and fir above, 

 of yellow pine below; many of their gorges set with thickets of scrub-oak and quak- 

 ing-asp. 



Along the base of the mountains stretches a belt of foot-hills, a region of which 

 the surface is broken into rounded or abrupt hills, from 100 to 1,000 feet in height, 

 generally composed of sedimentary rocks, very much disturbed, often pitched about 



