94 THE MOUNTAIN. 



which are large enough to impress any striking features on 

 the topography of this region, or to have caused the coal to 

 be removed from their lines of elevation, are not generally 

 of any considerable size, further than forty miles into the 

 basin across the strata. 



Between these higher ranges of ridges are the wide and 

 irregular valleys, already described in the topographical part 

 of this chapter, scarcely conveying the idea or impression of 

 valleys, from their surfaces being perpetually broken up by 

 hills of greater or less magnitude. Through these basins the 

 crops of the coal-seams are found on the hill-sides and in 

 the ravines, extending from hill to hill, and rising gradually 

 toward the anticlinal axes, or plunging below the water- 

 courses and levels of denudation, toward the invisible ranges 

 of the synclinal troughs. 



The smaller valleys, or minor depressions, are generally 

 the courses of the streams which drain this district, and are 

 extremely irregular, presenting every imaginable variety of 

 configuration of surface. 



This fact alone gives variety unequaled, and an element 

 of surprise and enchantment to the landscapes of this inte- 

 resting region. 



The coal series, designated and characterized as a separate 

 formation, is made up, as has been already said, of a variety 

 of sandstones, slates, and shales, with limestone and coal- 

 seams, forming, as will be easily understood by reference to 

 the vertical section, the upper part of that majestic pile of 

 sedimentary rocks constituting almost the entire geological 

 structure of Pennsylvania, as well as a considerable portion 

 of the Atlantic and Middle United States. 



In Pennsylvania the region made of these coal rocks pre- 

 sents throughout the broken and hilly surface already de- 

 scribed; the higher lines, or chains of hills, showing the 

 position of the geological masses below, and revealing the 

 ranges of fracture, and of elevation, and depression; the 

 system of drainage also showing the lines of washing, to- 

 ward the larger valleys of denudation, in which the creeks 



