700 [Nov.7, 
probably formed long before the Luray Cavern, which is excavated out of 
the same limestone formation. The bridge seems to be located in the 
centre of a gentle basin or syncline in the strata, which may account for 
the roof of the ancient cavern being left at this special point. The height 
of the bridge has evidently been much augmented by a lowering of the 
bed of Cedar creek through the agency of chemical and mechanical 
erosion after the destruction of the original cavern. The height of the 
cavity at the point where the bridge now exis!s being in consequence very 
much less than the present height of intrados of the bridge arch. 
The elevation above ocean level of the railroad track at Natural Bridge 
Station on the Shenandoah Valley R. R., is 760 feet, and the elevation of 
Cedar creek under the north face of the bridge arch is 915 feet, as deter- 
mined by two independent lines of barometric levels which I ran from the 
railroad station to the bridge. The height of the crown of the arch on the 
north side at the ‘“‘Lookout Point’”’ is 188 feet above the creek, measured 
with a cotton twine, which was the only line of the required length which 
could be obtained. The same measured by barometer (Short and Mason 
aluminium aneroid), was determined as 186 feet. Neither of these methods 
of measurements are sufficiently exact to permit of a final statement, but 
are of interest in the absence of more definite data. The thickness of the 
arch under the crown on the north side is approximately 46 feet, and on 
the south side 36 feet. ‘ 
Much has been written and published about this Natural Bridge since 
the appearance, a century ago, of the Travels of the Marquis de Chastellux 
in North America, in 1780-2, but there appears to be a lack of a complete 
description of the bridge and its surroundings which is readily available, 
which would prove of special value to the topographer and geologist. 
Stated Meeting, November 7, 1884. 
Present, 18 members. 
President, Mr. FRALEY, in the Chair. 
Col. Ludlow, Dr. Randolph, and Mr. Dickson, new members, 
were introduced to the presiding officer and took their seats, 
Letters of acknowledgment were received from the Royal 
Academy at Madrid (XVI, i, 118, 114); the Society of Antiqua- 
ries of London (415); and the Maine Historical Society (115). 
A letter of envoy was received from the Meteorological 
Office, Royal Society, London. ° 
