Mesozoic and Cccnozoic Geology and Palaeontology. 61 



some eight miles below the Comanche Ford, the sides of a deep washed 

 ravine bring to view the successive and relative thickness of the rocks. 

 We here see the upper members of tiae Cretaceous rocks forming the 

 tabled summits of the adjoining mountains, and marked by frequent 

 Cretaceous fossils, resting on a bed of igneous trap-form rock 50 to 80 

 feet thick, this again overlaying the closer layers of the limestone strata 

 below. 



The gigantic canon of San Carlos, through which for ten miles the 

 Rio Grande, pursuing a nearly due east course, makes its way, pre- 

 sents unbroken walls of Cretaceous limestone. The course of the 

 river cutting the strata in a line directly opposed to the dip, there is a 

 constantly increasing elevation of the canon walls. These walls com- 

 mence with a height of between 200 and 300 feet; but the fall of the 

 water, combined with the rise of the strata, develops, in the course of 

 ten miles, a clear perpendicular height of at least 1,500 feet above the 

 river level. 



A faint conception only can be formed from these facts of the truly 

 Awful character of this chasm. Its course can be marked along the 

 mountain slope in a regular zigzag line, terminating by an opening 

 cleft, which rises high and clear above the surrounding mountain 

 ranges. The surface of the ground adjoining the river bank is a 

 slightly broken slope, extending to the east, and showing a continuous 

 development of the range to the north and south. The general surface 

 presents no indication of a river course, and you are not aware of its 

 presence till jou stand suddenly on its abrupt brink; even here the 

 running water is not alwa3-s visible, unless advantage be taken of the 

 projecting points, forming angles, along the general course of the 

 river. From this dizz\^ height the stream below looks like a mere 

 thread, passing in whirling eddies, or foaming over broken rapids; a 

 stone hurled from above into this chasm passes completely out of 

 sight behind the over-hanging ledges, and one can often count thirty 

 before the last deadened splash announces that it has reached the 

 river bed. From the point formed b}'- its last projecting ledges the 

 view is grand be3'ond all conception. You can here trace backward 

 the line of the immense chasm, which marks the course of the river, 

 till it emerges from its stupendous outlet. 



The mountain range forming the San Vincente canon, lower down 

 the Rio Grande, is exclusively Cretaceous. The eastern slope of the 

 Sierra Carmel shows the Cretaceous limestone inclining eastward at 

 an angle of about 20°; and the Cretaceous continues to be exposed al- 

 most uninterruptedly to the mouth of the Pecos river. From here to 



