284 Prof. Sedgwick and Mr. Murchison 



ever, state generally, that the Cornish raised beaches, are not all at one level, 

 nor of one character; and though they are all of the modern aera, they do not 

 belong to one epoch of elevation. They may be divided into 



1st. High shingle beaches, resembling the large rounded blocks so con- 

 stantly seen at the highest water level on all rocky shores. 



2dly. Mid-water beaches, composed of rounded pebbles, broken shells, &c. 

 exactly resembling materials washed up between high, and low water mark. 

 These accumulations are seldom regularly bedded, but have more or less of a 

 confused aspect. 



3dly. Low-water beaches. These have originally extended from a few feet 

 above low water, to an indefinite depth ; and, consequently, such masses are 

 regularly stratified, being made up of small gravel, alternating with sand, 

 single shells, and beds of shells, all similar to living species of the present coast. 



Such appears to us a natural division of these beach deposits ; and the Cor- 

 nish coast offers fine examples of each class. 



The phenomena, described by Mr. Carne, near the Land's End* (viz. large 

 rounded blocks, 30 or 40 feet high, in the successive bays and headlands, and 

 nearly all at the same level), were observed by one of the authors in 1828 ; 

 but, misled by the diluvian theory, he then misinterpreted their meaning. 

 But we can now perfectly understand how these high-water shingles should 

 appear by themselves, the other parts of the beach having been washed away. 

 The shingle beach at Plymouth may be mentioned as an example of the 

 second class. But the third class is incomparably the most interesting; be- 

 cause it conducts us to the old water-worn rocks, once washed by the sea, and 

 forming the actual ledge on which these low-water beaches rest; and also 

 because, having been partially deposited under the sea, it is charged with 

 abundance of marine spoils, and sometimes with regular beds of sea-shells. 

 Of course, the shells, as in beaches of the present day, were for the most part 

 dead, when entangled in the layers of sand ; but in some cases, we have a 

 proof, that the animals were not dead at the time they were first entangled in 

 the deposit where we find them ; though now raised many feet above the 

 highest tidal level. 



Such examples may be seen north of St. Ives Bay, and south of New Quay, 

 and at several other parts of the north coast of Cornwall f. Now in most cases 

 of raised beaches, we may infer, d priori, that the coast was shelving and shal- 

 low before their elevation ; for such beaches could adhere but imperfectly to 

 an abrupt shore ; and if adherent for a short time, would soon be washed away. 

 Hence it is, that where we find raised beaches, we may look for extensive 



* Trans. Roy. Geol. Soc. of Cornwall, vol. iii. p. 229, et seq. + Ibid., vol. iv. p. 259. 



