72 INLAND SEA-CLIFFS. |>h. VI 



faced, wherever, in consequence of the altered state of the tides and cur- 

 rents, the sea has receded for a few centuries. We see the cliffs crumble 

 down in a few years if composed of sand or clay, and soon reduced to a 

 gentle slope. If there were shells on the beach they decompose, and 

 their materials are washed away, after which the sand and shingle may 

 resemble any other alluviums scattered over the interior. 



The features of an ancient shore may sometimes be concealed by the 

 growth of trees and shrubs, or by a covering of blown sand, a good ex- 

 ample of which occurs a few miles west from Dax, near Bourdeaux, in 

 the south of France. About twelve miles inland, a steep bank may be 

 traced running in a direction nearly northeast and southwest, or parallel 

 to the contiguous coast. This sudden fall of about 50 feet conducts us 

 from the higher platform of the Landes to a lower plain which extends 



Fig. 92. 



Sea, 



-s 



Section of inland cliff at Abesse, near Dax. 

 a. Sard of the Landes. b. Limestone. c. Clay. 



to the sea. The outline of the ground suggested to me, as it would do 

 to every geologist, the opinion that the bank in question was once a sea- 

 cliff, when the whole country stood at a lower level. But this is no 

 longer matter of conjecture, for, in making excavations in 1830 for the 

 foundation of a building at Abesse, a quantity of loose sand, which 

 formed the slope d e, was removed ; and a perpendicular cliff, about 50 

 feet in height, which had hitherto been protected from the agency of the 

 elements, was exposed. At the bottom appeared the limestone 6, con- 

 taining tertiary shells and corals, immediately below it the clay c, and 

 above it the usual tertiary sand a, of the department of the Landes. At 

 the base of the precipice were seen large partially rounded masses of 

 rock, evidently detached from the stratum b. The face of the limestone 

 was hollowed out and weathered into such forms as are seen in the cal- 

 careous cliffs of the adjoining coast, especially at Biaritz, near Bayonne. 

 It is evident that, when this country stood at a somewhat lower level, the 

 sea advanced along the surface of the argillaceous stratum c, which, from 

 its yielding nature, favored the waste by allowing the more solid super- 

 incumbent stone b to be readily undermined. Afterwards, when the 

 country had been elevated, part of the sand, a, fell down, or was drifted 

 by the winds, so as to form the talus, d e, which masked the inland cliff 

 until it was artificially laid open to view. 



When we are considering the various causes which, in the course of 

 ages, may efface the characters of an ancient sea-coast, earthquakes must 

 not be forgotten. During violent shocks, steep and overhanging cliffs 

 are often thrown down and become a heap of ruins. Sometimes une- 

 qual movements of upheaval or depression entirely destroy that horizon- 



