164 Prof. Backers Report on the U. S. Coast Survey. 



m r 



set with reference to the prevailing winds. At the same time, 

 he regards the whid as having but small influence, as a first cause, 

 in effecting these changes. The sand seems to be first thrown 

 up by heavy seas and during storms, afterwardSj when dry, to be 

 carried about by the wind and deposited, until so near the level 

 of high water as to be prevented by its dampness from rising 

 with the winds. 



In the western part of Mississippi sound, the water has changed 

 from salt to fresh, owing to a crevasse through which the water of 

 the Mississippi river enters Lake PonchartraiUj and thence reaches 

 the Sound. The shell fish have been destroyed, and, if the cre- 

 vasse continue, the character of that region may change materially- 



The character, as Well as the configuration of the bottom of 

 the ocean is ascertained, and laid down on the charts of the Sur- 

 vey. Specimens of the bottom, obtained by soundin£;s off the 

 coast, are regularly collected and preserved. Their variety will 

 often afford the mariner the means of relying on his lead for his 

 position. The materials brought up in the deep sea soundings 

 have, under the microscope, proved of the highest scientific in- 

 terest. They have been already discussed by Professors Bailey 

 and Agassiz. 



Experiments have been made to ascertain the amount of un- 

 certainty in ocean soundings, under different circumstances. 

 The results obtained are of practical importance, as deciding the 

 degree of accuracy necessary to be arrived at in observing the 

 tides for the correction of soundings. 



The observations of local attraction on board the iron steamer 

 Jefferson have given the curious result of a difference not amount- 

 ing to as much as four degrees, when heading towards opposite 

 points of the compass. It is not known that any such case has 

 ever before been observed. 



In no point of view perhaps, can the results of the survey be 

 made available for purposes of greater immediate importance, by 

 the government to whom they are submitted, than in the estab- 

 lishment of light-houses, and the like facilities, for the guidance 

 of our navigation. A wise selection is far more advantageous 

 than an undue multiplication of such works. Accordingly, the 

 attention of the parties employed in the various sections of the 

 Coast Survey is constantly and minutely directed to the examin- 

 ation and selection of suitable points for light-houses, beacons, 

 and buoys, and the determination of tlie best modes of construc- 

 tion for attaining the objects in view at the different localities. 

 We trust that the attention of our government will not slumber 

 over this subject, but that a judicious use of the knowledge thus 

 acquired will cause to be devised and carried out, a system which 

 shall lend new wings to our commerce, alleviate the hardships 

 and lessen the dangers of the mariner, and lighten the hearts of 

 those at home, whose fancy tracks in dreams his dangerous path. 



