Irregularities of the Earth's Surface. 



149 



II. On the Irregularities of the Earth's Surface, and the Probable 

 Mean Line of the Terraqueous Circumference. By William 

 Rhind, Esq. 



The periphery of the earth's surface consists of land and 

 water at different levels, and the question may be suggested 

 — whether is the surface of the ocean, or the mean level of 

 the land, the true line of the earth's circumference, or, in 

 other words, what is really the medium line of the irregu- 

 larities of the earth's surface ? 



Though our knowledge of the sea-bottom is yet very 

 limited, yet the investigations of recent years have added 

 very considerably to this knowledge. The soundings of Sir 

 James Koss in various parts of the ocean have disclosed in- 

 teresting facts concerning its depth and temperature ; these 

 were followed by other British and American navigators, 

 and the whole has been collected and published by the 

 labours of Lieutenant Maury. From these and other re- 

 searches, we find that the earth's superficies, both under the 

 ocean and above it, presents an exceedingly irregular form, 

 consisting of a series of elevations and depressions. On this 

 irregular surface are diffused the waters of the ocean, 

 spreading over and concealing from view more than two- 

 thirds of the superficies, while the higher portions only, 

 amounting to somewhat less than one-third, appear as dry 

 land. The greater amount of soundings have been made 

 in the Atlantic Ocean, and thus we have become better 

 acquainted with its bottom than with that of the other 

 oceans of the globe. A section from the Cape de Verd 

 Islands, on the coast of Africa, to the mainland of South 

 America, gives soundings of 17,000 and 22,800 feet. A 

 section south of Newfoundland gives the greatest depth yet 

 authentically ascertained as 27,180 feet. Further north, in 

 the line of the late electric telegraph from Ireland to New- 

 foundland, the depths are 10,000, 11,000, and 12,000 feet. 

 On taking a mean of twenty-seven soundings in various 

 parts of the Atlantic, and rejecting a few doubtful ones, the 

 ^aean depth of this ocean is indicated as 13,100 feet, or two 

 j&d a half miles. Soundings in the Pacific, also, indicate 



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