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 Ross 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 tw^o- 
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 
mean depth of this ocean is indicated as 13,100 feet, or two 
and a half miles. Soundings in the Pacific, also, indicate 
