58 THE BERMUDA ISLANDS. 



consequently there is no direct way of ascertaining in what 

 period the tests of a given column of water are replenished. 

 But manifestly, there can be no more rapid accumulation of 

 the calcareous ooze than there is lime-carbonate suspended in 

 the sea; and again, the quantity of lime-carbonate so sus- 

 pended must depend upon the quantity of the formative 

 material contained in the sea the quantity of lime carried in 

 by the rivers, and any residual or surplus quantity that might 

 be already existing. Now, it would seem from careful obser- 

 vation made on many of the most important rivers of the 

 globe that the quantity of lime carried out by them into the 

 sea annually is about one-sixth that of their suspended sedi- 

 ment, which would cover the sea-bottom, if precipitated at a 

 rate proportional to that of the removal of continental sedi- 

 ment one foot in 3000 years to a depth of about 7 ^ inch. 

 Assuming that, one-half of this amount is used by the Fora- 

 minifera for the construction of their shells, the rest being 

 taken up by the mollusks, corals, etc., then the foraminiferal 

 accumulation from this source would be the ^ part of an 

 inch annually, or very nearly the amount that would accumu- 

 late from the droppings contained in the 600-foot column of 

 water, as deduced from Mr. Murray's determination. At this 

 extremely slow rate of accumulation, it would require a period 

 of 100,000 years to build up the thickness of a single foot! 

 Naturally along coast-lines, where the molluscous animals 

 largely contribute to the general growing mass, and where inor- 

 ganic sedimentation is unusually brisk, the process of upgrowth 

 may be comparatively rapid, especially in the trend of powerful 

 oceanic currents. A condition of this kind seems to obtain 

 along the Floridian coast, and it is not unlikely, as has 

 been suggested by A. Agassiz, that the Florida banks have 

 been built up largely in the manner above described. But the 

 conditions become very different when the oceanic abyss, such 

 as the central Pacific, is substituted for a comparatively shallow 

 coast-line. Indeed, even in the case of the Floridian banks it 

 is doubtful if most of their upgrowth is not really due to 



