30 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
Hatteras more than 200 miles west of its present position. This 
horizon is marked by an immense sand reef, still retaining its wind 
and wave marks, and rising to a height of more than 500 feet above 
tide, the reef itself being at least 100 feet deep and many miles in 
length. The sea must have remained at this level for a very long 
period. 
But Hatteras is not a modern phenomenon. It is at least as old 
as the cretaceous; the quaternary as well as the tertiary of this 
coast region of North Carolina are laid down upon an eroded 
surface of cretaceous rock, while the artesian borings, at Charleston, 
reach this formation at 700 feet, and at the mouth of the Chesa- 
peake they do not seem to have touched it at 1,000 feet. 
Mr. Warp remarked that, in traversing the Jericho canal of the 
Dismal Swamp in a row boat, he had observed an outward flow at 
both ends of the canal, showing that, by continuous water passage, 
a divide was crossed between Lake Drummond and the James river. 
He criticised the doctrine taught in text-books and popular writ- 
ings that the preservation of leaves in a fossil state is due ordinarily 
to river action and delta formation. More favorable conditions 
are to be found in swamps. 
Other remarks were made by Messrs. Durron and Hove. 
The second communication was by Mr. H. F. Waiine on 
TOPOGRAPHICAL INDICATIONS OF A FAULT NEAR HARPER'S FERRY. 
[ Abstract. ] 
A description was given of a break in the continuity of the Blue 
Ridge, where its disconnected portions, extending side by side for a 
few miles, are cut by the Potomac river, near Harper’s Ferry, the 
gorges so formed presenting a striking feature of the scenery. 
The two ridges, here about 12,000 feet apart, stretch for hundreds 
of miles in nearly parallel directions, one to the south and the 
other to the north; the latter being known in Pennsylvania as the 
South Mountain. ‘The strike of the rocks is parallel to the ridges, 
about N. 30° E., and the prevailing dip is eastward; averaging not 
more than 30°. The ridges are composed of hard sand-rock; 
the adjacent region, of lime-stone and other, rocks more easily dis- 
integrated or dissolved. 
Supposing the sand-rock of the Blue Ridge and South Mountains 
to have been originally a continuous formation, it will be readily 
