MATURE STAGE OF TOPOGRAPHY REACHED. 235 



great variety of form, from the cascade condition of the mountains to the 

 broad base-level condition of the river bottom. 



The ranges of level are not very great. From Fort Smith eastward the 

 Arkansas river falls at a rate of about a foot to the mile, the altitudes being, 

 at Fort Smith, about 430 feet ; at Dardanelle, about 320 feet ; at Little 

 Rock, about 260 feet. The highest summit is that of Magazine mountain, 

 which reaches an altitude of 2,850 feet. 



Mountains. — The mountains vary in profile and plan according to the 

 position and character of the strata composing them. The Boston mountain 

 area on the north may be classed as an elevated plateau cut by deeply corraded 

 channels. The general altitude is between 1,000 and 2,000 feet. The surface 

 is undulating and, at a number of points, rises to summits several hundred 

 feet above the surrounding country. The component rocks are grits, sand- 

 stones and shales ; and in the northern portion limestones appear near the 

 base. These rocks lie generally in a horizontal or slightly inclined attitude. 

 Towards the south the mountain mass in places slopes gradually to the level 

 of the river, but elsewhere it rises abruptly from the valley, presenting 

 bold escarpments of massive sandstone along several benches ; the mountain 

 front is notched by ravines and hollows setting back into the plateau. 



The mountains immediately south of the Arkansas river include the Sugar 

 Loaf mountain, Poteau mountain and White Oak mountain. These are 

 members of a system which extends westward into Indian Territory, and 

 eastward, with somewhat irregular grouping, to the Arkansas river at and 

 below Dardanelle, including such ranges as the Petit Jean and the Maga- 

 zine, and such outlying masses as Mount Nebo and the Short mountains. 

 The trend is approximately east-and-west in all cases. These mountains are 

 of horizontal or flat synclinal structure, and are made up of alternating 

 beds of sandstones and shales. They are, in many cases, typical illustrations 

 of mountains of circumdenudation, notably Sugar Loaf mountain, Magazine 

 mountain. Spring mountain and Mount Nebo. The elevation of the summits 

 varies from about 1,000 feet to 2,850 feet above tide. They have generally 

 very steep slopes, though these are frequently broken by benches formed by 

 resisting layers of hard sandstone, which often stand out from the mountain 

 side in abrupt escarpments. The crest is often a flat table-land, and this, 

 as well as the benches on the sides, are frequently cultivated. Timber extends 

 to the very summits of these mountains, though at the higher altitudes it is 

 small and stunted. 



Further southward, as the region of greater disturbance is approached, the 

 mountains consist of steep-dipping strata, more or less metamorphosed ; such 

 mountains are those of the Rich Fork, Black Fork and Fourche ranges. 



Ridges and Mesas, — The mountains are the more prominent, the grander 

 features of the topography ; but the ridges and mesas of this area far exceed 



