OF THE LEVEL OF THE SEA. 59 



tion of 400 feet. Proofs of such changes have also been ob- 

 served in the Channel Islands and on the opposite shores of 

 the Continent, all probably referable to the same geological 

 epoch. 



These marine beds have been discovered at every eleva- 

 tion, from that of the present level of the sea to a height of 

 at least 400 feet above it ; and in the solitary instance of 

 Moel Tryfane shells have been found at the height of 1400 

 feet ; but as the cause of their occurrence in that situation 

 is doubtful, we may conclude that the highest elevation at 

 which proofs of such recent changes have been hitherto dis- 

 covered is limited to 400 feet. 



At this height Mr Gilbertson found sea-shells in stratified 

 beds of gravel and sand near Preston in Lancashire. Mr 

 M urchieson,* who visited this locality, observed " similar 

 phenomena over a very considerable tract of country occu- 

 pying the ancient estuary of the Kibble. Sands, marls, and 

 gravels, occasionally forming terraces, are spread over this 

 great area, sometimes in finely laminated beds, but for the 

 most part loosely aggregated, and bearing a great resem- 

 blance to the arrangement of the same materials now in the 

 act of formation on the adjoining shores. Many of the 

 shells found in these beds far inland, and at heights extend- 

 ing to 300 feet above the sea, are perfectly identical with 

 existing species. 1 '' Mr Murchison justly infers, that such 

 appearances must be ascribed to actual elevation rather than 

 to the action of diluvial currents. Sea-shells were found by 

 Mr John Craig, mineral surveyor, at Airdrie about ten miles 

 to the east of Glasgow, at the height of about 350 feet ; they 

 were found between a mass of blue till and a bed of yellow 

 stratified clay, which rested upon it. Mr Craig was inclin- 

 ed to suppose they belonged to the till, the shells having 

 * Address to Geological Society, Feb. 1832. 



