BITUMINOUS AND ANTHRACITIC. 445 



sight into the physical conditions which accompanied the pro- 

 duction of these sti'ata. 



Of the facts connected with the range of the individual coal- 

 seams, that of their prodigious extent is, itself, one of the most 

 surprising and instructive. As a general rule, this wide expan- 

 sion characterizes all the beds of both the bituminous and anthra- 

 citic basins. It is true, that many seams possess a compai-atively 

 local range, but not a few of those which, on first examination, ap- 

 pear of circumscribed extent, cover in reality a very wide area, the 

 error respecting them being caused by fluctuations of thickness, 

 or by their occasionally thinning out and reappearing. Among 

 those which manifest gi-eat permanency as to thickness, the vast 

 range of some of the larger ones is truly extraordinary. Let us 

 trace, for example, the great bed, which occurs so finely exposed 

 at Pittsbm-g, and along nearly the whole length of the Mononga- 

 hela river, and which I have called the Pittsburg seam. The 

 high position which this bed occupies in the formation, and the 

 nearly horizontal attitude of all the striata, combine to expose it 

 very extensively to observation, while its great size, and the ex- 

 cellence of the coal, have caused it to be generally mined. After 

 identifying and tracing it from basin to basin in Pennsylvania, I 

 have been furnished with much information in relation to its 

 limits and features in Virginia and Ohio, by my brother and Mr. 

 Briggs. Guided by the data thus collected, I have been enabled 

 to determine its area and boundaries with very considerable ac- 

 curacy. The limits of this bed, as at present known, are nearly 

 as follows. That portion, by far the largest part, which is con- 

 tained in the great w^estern basin, has its northern termination in 

 Indiana county, in Pennsylvania, and its southwestern on the 

 Ohio river, below Guyandotte. The general southeastern out- 

 crop ranges along the western foot of the Chestnut ridge, or 

 West Laurel hill, from Indiana county to Tygart's river, in 

 Virginia. It here alters its strike from south-southwest to a direc- 

 tion more nearly south, passing a little west of and parallel to, 

 Buchanan's river, until it nearly gains the head-waters of the 

 Monongahela. From this point its course is more winding, but 

 the general direction is a little west of southwest to the Great 



