4 BULLETIX 171, UNITED STATES NATIONAL, MUSEUM 



Perhaps the oldest surface recognized, which has been referred to 

 the Schooley Plain, includes the higher portions of the Allegheny 

 Mountain section of the Appalachian Plateaus. A somewhat lower 

 level may be represented by the crest of Wills Mountain (see pi. 1) 

 just east of Cumberland Cave and having an elevation vaiying from 

 1,400 feet to 1,800 feet. A still lower surface is beheved to be indi- 

 cated by the crest of Shriver Ridge just north of the town of Cumber- 

 land and by a spur of Kjiobly Mountain to the south of the town. 

 W. B. Clark and E. B. Mathews (1906, p. 89) correlated these ridge 

 crests with the Harrisburg surface, and Cleveland Abbe, Jr. (1900, 

 p. 52), considered them as representing a surface which he called the 

 Shenandoah Plain. The ridges have an elevation of about 1,100 

 feet near the Potomac River, and if the surface represented were 

 extended up Wills Creek Valley at the present stream gradient it 

 would have an elevation of about 1,200 feet at Cumberland Cave. 

 It may be represented, as suggested by Clark and Mathews, by the 

 ridge west of Wills Moimtain, in which Cumberland Cave is located. 

 This ridge crest varies in elevation from about 1,040 feet near the cave 

 to about 1,300 feet farther south. The elevation of the cave deposit, 

 as determined by O. P. Hay (1923) is 837 feet. Assuming practically 

 no gradient for the surface between Cumberland and Cumberland 

 Cave, we have a minimum difference of nearly 300 feet between the 

 elevation of the cave and that of the surface. 



During later stream history (Abbe, 1900) two important terraces 

 were developed in the vicinity of Cumberland at elevations of about 

 800 feet and 650-700 feet. The higher of these may have had an 

 elevation of about 900 feet on the spur in which the cave is located. 

 This is probably very close to the elevation at which the cave mouth 

 was located. The lower terrace may have been 750-800 feet in 

 elevation near the cave. This level appears to be slightly lower than 

 the cave deposit. It seems evident that the fossil material did not 

 accumulate until cutting by Wills Creek had at least reached the 

 stage represented by the higher terrace, and probably at a somewhat 

 later date when the drainage system had dissected this surface. 



