262 The American Geologist. May, isoo 
the southeastern portion are the elevated prairie lands of the 
Llano Estacado,changing in the northwest to the true plateau, 
from which platform rise the mountains of the territory ranges, 
chains and isolated peaks. The mountain topography is not 
so striking in this territory as it is in the more northern por- 
tions of the Rocky mountain area; but in northern New 
Mexico are the lofty Taos and other ranges, spurs of the great 
Colorado system. The trend of all these ranges, with a few 
unimportant exceptions, is generally north and south. The 
valleys between the mountain ranges are broad, shallow plat- 
eau valleys, out of which the peaks and ranges apj^ear to rise 
abruptly. 
The rain that falls upon New Mexico finds its way into two 
oceans by mean^ of three large arteries. . The Continental 
Divide in the western portion sheds water into the Colorado 
on the west and the Rio Grande on the east. The Taos moun- 
tains near the Colorado state line form the divide between 
some of the head waters of the Rio Grande and the Canadian, 
one of the tributaries to the Arkansas. The Pecos, the chief 
branch of the Rio Grande also rises on the eastern slope of the 
Taos range and is separated from the Canadian by a low plateau 
divide. Nine-tenths of New Mexico lies within the drainage 
area of the Rio Grande or its tributary the Pecos ; and the 
other two systems deserve mention simply in consideration 
of the drainage of this territory. 
The history of these rivers has been interesting and compli- 
cated, yet the complication has not been such as to obscure 
the general changes that have taken place. A detailed history 
would demand a much closer study than I have been able to 
give and I shall not attempt to do more than state some of the 
most striking changes that they have undergone in the course 
of their development. 
Many of the American rivers have existed as drainage sys- 
tems through long geological ages and are by this time topo- 
graphically as well as geologicall}-^ old. The Rio Grande is 
both topographically and geologically young, and the appear- 
ance of youth is increased by certain accidents which have 
rejuvenated it. Moreover there are two sections of the Rio 
Grande and of each of its tributaries, one of which is much older 
than the other. It is plainly evident that the valleys of 
erosion in the mountains are much older than those on the 
