1836.] ' the Advancement of Science. 193 



so, that the mariner may know any half hour the banks 

 which might be crossed, thus pointing out what was dan- 

 gerous, and when it ceased to be so, a matter of great relief 

 to the mariner. Lieutenant Denham complimented the dock 

 trustees of Liverpool, for their munificent expenditure, in en- 

 abling him to prosecute his object, and dwelt with particular 

 energy on the great liberality of Sir John Tobin. Lieutenant 

 Denham suggested the utility of establishing a half tide 

 level at each port, to point out the soundings of banks at 

 the half tide along the continuous shore. He next alluded 

 to the error which had been nearly committed, in cutting a 

 canal fi*om Bridgewater to the sea, when there were tides 

 from a fifty feet level to eighteen feet. He observed, that 

 if the distance from the earth's centre to the half tide level 

 was calculated, it would form a correct base for ascertain- 

 ing the heights of the land. It would form a matter for 

 consideration if the influence of the sun and moon on the 

 tides were withdrawn, whether or not the water would re- 

 -cede to the half- tide level. 



Professor Sedgwick congratulated the town of Liverpool 

 on the importance of this discovery, and the possession of 

 such a map and tables. 



Sir John Tobin offered a few observations complimentary 

 to the exertions of Lieutenant Denham. 



Mr. Griffith moved the especial thanks of the Section to 

 Lieutenant Denham. 



Mr. Murchison said, this showed the intimate connexion 

 between geology and geography. If this subject was fol- 

 lowed up with that spirited enterprize displayed by such 

 gentlemen as Sir John Tobin, and others, the encroach- 

 ments of the sea in one place, and the increase of land in 

 another, and the rate of that increase and decrease might 

 yet be defined. 



The communication of Lieutenant Denham is considered 

 as one of the most important subjects in physical geography 

 yet submitted. 



Thursday^ August l^th, — 7. M. Agassiz laid before the 

 Association an additional number of his work on fossil fishes ; 

 and, in an eloquent address, he gave a summary of the geo- 

 graphical conclusions to which the study of fossil fishes had 



VOL. II. o 



