Stevenson.] o^ [August 20, 



Notes respecting a Be-eroded Channel-way. By John J. Stevenson, Pro- 

 fessor of Geology in the University of the City of Neio York. {With 

 three wood cuts. ) 



{Bead before the American Philosophical Society, Aug. 20, 1880.) 



The north branch of the Canadian river is formed near west longitude 

 104° 30' at about 25 miles south from the northern boundary of New 

 Mexico by two small streams, which rise in the Raton hills and drain much 

 of the Trinidad Coal Field. Within 25 miles, the river enters a caiion, 

 which deepens rapidly until, at 50 miles from its head, its nearly vertical 

 walls are almost 1100 feet high, while the width of the gorge at the bottom 

 varies from 150 to 800 feet. Thus far no important tributary enters the 

 river in the canon, but the petty side-canons show that at some time or 

 other much water must have flowed in from the Canadian plains. At 

 probably 50 miles from the head of the canon the Canadian river is in- 

 creased by the Mora river, which rises on the east slope of the Las Vegas 

 range and flows eastward to the Canadian. Its canon becomes close at a 

 little way south from Fort Union, and thence to the Canadian the river 

 flows at the bottom of a gorge with bold vertical walls, becoming higher 

 as the stream descends, until at the mouth of the canon they rise to 1090 

 feet above the "bottom," Avhere some half savage Mexicans gain a scanty 

 livelihood by cultivating little patches of corn and melons. 



Both canons have the hard Upper Dakota sandstone as their rim, and 

 that rock is the surface rock of the plains between the canons, where a few 

 relics of the Middle Cretaceous beds remain, protected by a plate of basalt 

 which covers the Low Mesas or Table hills. 



An extinct volcano, at 7 miles east from Fort Union, forms the southern 

 extremity of the Turkey mountains — the Gallinas hills of Dr. Newberry's 

 San Juan report — a curious qua-qua-versal, which deserves mttch closer 

 study than could be given to it by either Dr. Newberry or myself. The 

 volcano has been visited by Dr. Newberry, Dr. LeConte, Dr. Hayden and 

 the writer. The crater still retains its form and the rim is bi'okeu only on 

 the southern side, an imperfection due, perhaps, in some measure to erosion, 

 but in greater part to the pressure of the lava. The eruption to which 

 this mountain owes its origin occurred in the later Tertiary, and the lava 

 is basaltic. 



The basalt extends northward but a very little distance and the flow was 

 toward the south through the breach in the crater. The lava was followed 

 from the breach directly to the Mora caiion, the passage beginning along an 

 arroyo or dry water course, where the basalt rests on Upper Dakota sand- 

 stone, though occasionally a little debris intervenes. At one locality, some 

 tufaceous limestone, characteristic of the Santa Fe Marls, belonging to the 

 Loup River epoch, is included in the debris. 



Entering the Mora canon, the basalt followed the gorge to its mouth, and 

 was in such volume as to flow up the Canadian caiion to a distance of near- 



