108 EXPLOEING EXPEDITION FEOM SANTA FE 



which its waters poured in a cascade. This is shown by the gravel terrace which, 

 east of it, rises to the height of 300 feet above the present bed of the stream. The 

 strata composing it are set at an angle of about 35, and are the equivalents of those 

 which form the greater part of the Mesa Verde. As affording a more complete section 

 of the Upper Cretaceous rocks in this region than any I had before observed, I ex- 

 amined them with some care, and found them to consist of the following elements : 



Section of rocks composing the Creston. 



Foot. 



1. Yellowish-brown calcareous sandstone, generally thick-bedded 2GO 



2. Yellowish-brown sandy shale, with thin bands of sandstone and beds of lig- 



nite 150 



3. Yellowish sandy limestone, with strata of hard blue limestone ... 70 



4. Dove-colored and purplish shales, with beds of impure lignite 1 75 



5. Gray and purple shales, with bands of sandy limestone, and lines of concre- 



tions of umber-colored and purple iron-stones 200 



6. Brown calcareous sandstones 20 



7. Gray and purplish shales, with bands of ferruginous sandy limestone 170 



8. Yellowish-brown sandstones, whitish above 150 



9. Gray and blue shales, continuous with those of Camps 39 and 40. 



In this section, No. 1 is geologically the highest, and forms the most elevated por- 

 tion of the Creston. 



The shales of No. 9 immediately overlie the ferruginous limestone of Camp 39, 

 which contains so many Inocerami, fish-teeth, &c. 



The interval between these two groups represents the middle and upper portions 

 of the great group of shales which form the middle division of the Cretaceous system, 

 so often referred to in the preceding pages. 



As in the sections observed on the northern route, the bands of sandstone and fer- 

 ruginous sandy limestone are shown to be only local phenomena; since they sometimes 

 expand and assume great local importance, and again disappear and give place to a 

 nearly homogeneous mass of calcareous shales, 1,300 to 1,500 in thickness. 



Among the strata forming the Creston are several beds of lignite, of which one, 

 six feet thick, visible for many miles along the river, is unusually compact and pure ; 

 in its general appearance precisely resembling some of the coal strata of the Carbon- 

 iferous series. 



No fossils wore discovered in any of the rocks here exposed above the Inoccramus 

 limestone, but probably impressions of plants would be obtained from the shales over 

 the lignite beds, if time were given to search for them. 



From the Creston to the mouth of Canon Largo the banks of the San Juan are 

 composed throughout of the strata which have just been enumerated, lying in unbroken 

 sheets, with a gentle easterly dip. In these strata the valleys of the San Juan, La 

 Plata, and Animas have been deeply cut, and are bounded by abrupt, frequently per- 

 pendicular walls, the edges of table-lands, many hundred feet in height. The bottom- 

 lands of these valleys, though narrow, are fertile; sustaining a vigorous growth of grass, 



