the other extremity of this line, both of these mountains seem- 

 ing to be centres of action. 



The Ute Pass lies to the north of Pike's Peak, and is a very 

 beautiful and picturesque pass, cut out of the granite along 

 the course of the " Fontaine qui bouille," and is the road to 

 South Park, which comes to our notice next. 



South Park is a large area of depression, of the general 

 shape of an ellipse, having a diameter of 45 miles from north- 

 west to southeast, and of 35 miles from northeast to south- 

 west. Its area is about 1200 square miles. It is not a perfectly 

 level plain, but has a general slope from the northwest, 

 almost to the base of the Front Range, where lies the 

 bed of the Platte. This accounts for the curious drain- 

 age system of the Park, as a moment's glance at the map will 

 show. The rivers flow down the long slope of the western 

 side till they reach the short counterslope of the eastern side, 

 and then turning almost at a right angle flow to the north- 

 east. The general elevation of the Park is about 8000 feet, 

 though it reaches 10,000 feet in the western part, and goes 

 down to 7000 where the Platte canon pierces the Front 

 Range. It is surrounded by mountains, the bases of which 

 bear the marks of its having been at one time the bed of a 

 lake, not only from the form of the basin, but mainly from the 

 sedimentary rocks found deposited there. The surface of 

 the plain is quite irregular, being cut up by numerous low 

 ridges, which are generally parallel to each other. In the 

 central portion there are also cross-ridges of trachyte, show- 

 ing the existence of some extended fissure from which this 

 igneous overflow took place. Otherwise the sandstones of 

 the Park are very little disturbed. 



Before describing either the Park Range or the Sa watch, 

 let us look at the valley of the Arkansas, which lies between 

 them. It starts at the Tennessee Pass from a basin of gran- 

 ite, and has been formed partly by fissure and partly by 

 erosion. This valley varies in width from 8 to 10 miles, and 

 is cut down a hundred miles through the mountains to 

 Poncho Pass. It affords one of the finest fields for the study 

 of glacial action in the West. Dr. Hayden thinks * that the 



* U. S. Geog. and Geol. Survey, Hayden, 1873, p. 39. 



