28 THE VOYAGE OF H.M.S. CHALLENGER. 



what we know of the constancy of the position of continents and oceanic basins throughout 

 long geological periods." 



This argument cannot, I admit, be applied in all its rigour to the island of St. Paul, 

 because the period of its eruption, or of the upheaval which raised it above the level of 

 the Atlantic is unknown. Yet there exist between St. Paul and the nearest land-masses 

 depressions as great as those mentioned by Lyell ; and the soundings, particularly those 

 made by the Challenger Staff, have nowhere discovered in the vicinity of the island any- 

 thing that can be looked upon as even a trace of submergence. 1 



1 The soundings of the Challenger in this region, together with the results of the bottom temperatures, show 

 that St. Paul's Rocks are situated on a ridge connecting the " Dolphin " and " Challenger " ridges, and called 

 " Connecting Ridge." The depth on this ridge appears to be less than 2000 fathoms, and it runs in a W.N.W. 

 and E.S.E. direction from the rocks. A cove between the two largest islets has depths varying from 5 to 10 fathoms. 

 At the S.W. point there is a sunken rock which appeared to have 3 fathoms over it. When secured to one 

 of the north knobs the Challenger had 104 fathoms under her bow, 60 yards from the shore. The N.W. and S.E. 

 sides are steeper than the S.W. 500 fathoms are found at 1800 yards from the shore in the two former directions ; 

 whereas the 500 fathom line is at a distance of about 2 miles to the S.W. In approaching St. Paul's from the 

 east at a position lat. 3 8' N., long. 14 49' W., the bottom shows a level plateau, extending for 500 miles, the 

 depth being from 2300 to 2500 fathoms. After this there is a gradual ascent to a depth of 1500 fathoms, 150 miles 

 east of St. Paul's, then a depression to 1900 fathoms at a distance of 60 miles from the rocks. To the west and 

 northward of the rocks, at a distance of about 3 miles, there is a depth of 1425 fathoms. The soundings between 

 St. Paul's and Fernando Noronha show a deep ditch of 2475 fathoms to exist between these islands. J. M. 



