218 TRANSACTIONS OF THE [aPHIL 5, 



and brick-making is practised on a small scale. The valley 

 broadens ont below Port l\o])ublic. and, towards "Waynesboro 

 Junction, becomes much broken by numerous slate and limestone 

 hills and ridges, some of which attain considerable height, all 

 much inferior in altitude, however, to the Blue Kidge on the 

 east and the sandstone and conglomerate ridges of the Alle- 

 ghanies on the west. The uneven character of the region causes 

 great turbulence in the streams, numerous beautiful cascades oc- 

 curring among the hills. The streams have in many places cut 

 for themselves deeji and narrow gorges. 



The Natural Bridge, reached from Glenwood station on the 

 E. T. V. & Ga. K. K., is over the gorge of Cedar Creek, Avhich is 

 about thirty feet in average width and carries a considerable 

 body of water, flowing into the James Eiver about two miles be- 

 low the bridge. The magniticent natural arch has a span of 

 about 76 feet at its base; the south wall bulges out somewhat 

 ubove, so that at a height of fifty feet or so above the creek its 

 width is a few feet greater. The height of the loadway which 

 crosses the arch is about 221 feet above thecreek; the thickness of 

 rock at the crest is approximately 41 feet, so that the height of the 

 arch proper is about 188 feet.' Its width on top varies from thirty- 

 five to forty feet. The limestones are here bedded very nearly 

 horizontally, just above the bridge dipping only about 5° S. E. 

 Proceeding northwestwardly up tiie chasm, which maintains its 

 depth for half a mile in this direction, the southern inclination 

 of the beds becomes more pronounced, and at the cataract called 

 Lace Water Falls, 1^ miles up-stream, the dip is 40°-45° S. E.; 

 strike N. 40° E. Below the bridge the creek makes several bends, 

 and the caiion-liko character of the gorge is lost. Here the dip 

 is very slightly (5°) N. W., but a quarter mile below becomes 

 again S. E. about 37°, with a strike of N. 70° E. It will be 

 seen that the arch is in a gentle synclinal fold. In Science, 

 Jan. 2, 1885, Mr. C. A. Ashburner records his opinion that the 

 Bridge is the remaining top of a cave. 



Calcareous tufa is found in considerable quantities along the 

 banks of a little stream which empties into Cedar Creek just be- 

 low the arch. It incloses shells of mollusks, among them Helijc 

 alter nata and Physa, with twigs of Arbor Vitte {Thuja occideii- 

 talis), a tree which attains here enormous size — one with a trunk 

 circumference of 14^ feet was measured. This tufa is doubtless 

 of very recent deposition and is, perhaps, even yet accumulating. 

 Between tiie bridge and the railroad station (2| miles) there is a 

 broad belt of slate, dipping in general 70°-80° 8. E., doubtless 

 geologically overlying these limestones. At the station these are 



' Measurements barometrical. 



