_ 270 Proceedings of the Royal Physical Society. 
The entire ocean area is to the area of ocean drainage as 
3194 to 1. If, therefore, the quantity of lime-salts carried 
by rivers into the ocean is converted into the solid form and 
left over the entire ocean area, the formation of a thickness of 
one foot of limestone would require more than 133,000 years. 
There are, however, several causes which materially 
modify this result. One arises from the fact that the 
pressure of ocean water tends to dissolve calcareous 
organisms, beginning, as Professor Kendall has shown, with 
those which consist of aragonite, which are entirely dissolved 
before they descend from the surface-waters to a depth of 
1500 fathoms, and dissolving those which consist of calcite 
as the depth increases, so that below 2900 fathoms hardly 
any reaches the bottom. This redissolved lime again enters 
into circulation, and becomes diffused through the areas 
adjoining The area where this dissolution takes place, 
therefore, must be left cut of account. It may be roughly 
estimated to form about one-third of the entire ocean floor. 
There are other areas of the ocean, again, where the low 
temperature of the surface-water is unfavourable to the 
growth of large numbers of the pelagic lime-secreting 
organisms. Over this area, therefore, the supply of lime- 
salts in the sea-water is but little drawn upon. Then, again, 
although coral-reefs do undoubtedly represent a drain of a 
large quantity of the ocean lime-salts over an area perhaps 
extending even thousands of miles around, yet the solution 
of the limestone so formed goes on both at the surface and at 
some depths below, so that a fairly large proportion must 
find its way again into diffusion soon after it is fixed. 
Littoral shell banks, again, although they do represent so 
much solid material abstracted from the sea-water, yet 
undergo solution to some extent. Add to these sources the 
percentage of lime-salts dissolved by the ocean waters from 
the coast-line itself, delivery from submarine springs, and 
the lime dissolved out of basic tuff which happens to fall 
into the sea, and we seem to have taken into account every 
possible source whence lime-salts can find their way into the 
ocean. 
If we assume for the present purpose that the quantity of 
