60 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



Daniienberg^'' states that the Zach bed of the Zwickau (Saxony) 

 area is usually from i to 4.5 meters thick, but in the western part 

 of the field it is represented by 2 beds, separated by 8 meters of rock. 

 At Planitz in the southwest, the Planitzer bed is 10 meters thick and 

 the partings are very thin ; but these increase toward the north and 

 the 3 benches are in a vertical space of about 70 meters. He gives 

 illustrations of similar type from other coal fields. The familiar 

 instance is that described by Jukes. ^^ The Thick bed near Bilston 

 has about 30 feet of coal in 12 to 14 benches; followed northward, 

 the benches separate quickly, so that within 5 miles, one finds the 

 30 feet of coal distributed in a vertical section of 300 feet, the several 

 benches being independent coal beds separated by shales and sand- 

 stones. The Bottom and the New Mine beds divide in like manner. 

 Instances in other British fields have been described by Dugdale, 

 Howell, Bolton and several other observers. 



If one consider coal beds separated by considerable intervals he 

 finds equally interesting variations. The Upper Freeport and the 

 Pittsburgh are separated by 350 feet at the western outcrop in Ohio, 

 but that interval increases gradually toward the east until in Indiana 

 county of Pennsylvania it is 600 feet. The Pittsburgh and the 

 Waynesburg are 166 feet apart at the northern outcrop in Pennsyl- 

 vania, but that interval increases southwardly to more than 400 feet 

 in northern West Virginia. The increase is regular in the thickness 

 of intervening intervals between the Pittsburgh and Upper Freeport, 

 for, throughout, the Ames limestone holds its place approximately 

 midway between the coal beds ; but no such regularity of increase is 

 shown in the interval between the Pittsburgh and Waynesburg. An 

 excellent illustration of this irregularity is shown by comparison of 

 two sections given by W. G. Platt^^ from Armstrong county, Penn- 

 sylvania, which are as follows : 



These measurements are about 18 miles apart and the interval 

 between the Upper Freeport and the Lower Kittanning is practically 



'"A. Dannenberg, "Geologic der Steinkohlen Lager," 1911, pp. 211, 212. 

 "J. B. Jukes, "The South Staffordshire Coal Field," 2d ed., 1859, pp. 

 18, 19. 25, 26. 



='W. G. Piatt, Sea Geo!. Surv. Penn., Rep. Hs, 1880, pp. 215, 288. 



