NATURAL BRIDGES. 117 



In Limestone chiefly. 



Some of the cases already described are partly in limestone and some of those 

 now to be presented are partly in other rock ; but I shall bring those only under 

 the present division that are chiefly in limestone. 



1. Gulf at the Natural Ridge, in Rockbridge county, Virginia. — The width of this 

 gorge is 50 feet at bottom, and 90 feet at top; and the height of the bridge is 215 

 feet above the stream; its length I have not been able to ascertain. 



2. Gulf at the Natural Bridge, in Lee county, Virginia. — The walls here are 339 

 feet high, and the width of the stream from 35 to 55 feet. The length of the gulf 

 is not given, but the stream itself (Stock creek) is only a few miles long. 



3. Glenn s Falls, on Hudson River, Warren county, Neio York. — These are in black 

 limestone, and the gorge is of considerable depth and length, but though I have 

 visited the spot I have made no measurements. The height of the falls is about 

 50 feet. 



4. Trenton Falls, on West Canada Creek, in Oneida county, New York. — These 

 are also in the black Trenton limestone. Tbe gorge is very deep and extends for 

 at least two miles ; in which space are six cataracts. In passing through this 

 gorge I was much impressed with the power of water to wear away unyielding rock. 



5. St. Anthony's Falls, on the Mississippi- — The surface rock, over which this 

 large river, 1800 feet wide, is precipitated, is limestone, underlaid by friable sand- 

 stone. The latter easily disintegrates and undermines the limestone, which falls 

 at length by the force of gravity, piece after piece. In this manner have these 

 falls receded seven miles from the mouth of St. Peter's river. The fall of water at 

 present is only about 17 feet. From these falls to the mouth of the Wisconsin, 

 some 130 miles, the river passes through limestone, and has walls of rock, but 

 I have not met with any description definite enough to decide whether its bed has 

 been eroded all the way. 



6. Canada {little Cafion), of Santa Domingo, in Oaxaca, a province of Mexico. — 

 This gorge is from 10 to 30 feet wide, 25 miles long, and the immediate walls 300 

 feet high. Back from the river a mile, the mountains rise to the height of 2000 

 feet. This case was described to me by the late Mr. George R. Ferguson, who was 

 employed as an engineer upon the Tehuantepec railroad. The rock is limestone. 



7. The same gentleman mentioned another gorge on the river Tobasco, in the 

 province of Chiapas, in Mexico. It is 300 feet deep, but its length he could not 

 give. This also is in limestone. 



8. Defile of Karzan, on the Danube, on the borders of Hungary and Turkey, a 

 little above Orsova. — The river here is only about 600 feet wide, and the perpen- 

 dicular walls of limestone and slate, are 2000 feet high; and the water is 170 feet 

 deep. For many miles above this, a similar defile exists, and it is one of the most 

 remarkable gorges, or rather succession of gorges, between successive basins, on the 

 globe. — Murray's Handbook for Southern Germany, 5th edition, p. 511. 



9. The Via Mala, on the Rhine, near Thusis, in Switzerland. — The rocks are slate 

 and limestone, and the river is here compressed for the distance of four miles, into 



