1889-90.] Dr J. Murray & Mr R. Irvine on Coral Reefs. 101 
estimated at 925,866,500 tons. At this rate it would take 680,000 
years for the river drainage from the land to carry down an amount 
of calcium equal to that at present existing in solution in the whole 
ocean. Again, taking the “ Challenger ” deposits as a guide, the 
amount of calcium in these deposits, if they he 22 feet thick, 
is equal to the total amount of calcium in solution in the whole 
ocean at the present time. It follows from this that if the salinity 
of the ocean has remained the same as at present during the whole 
of this period, then it has taken about 680,000 years for the deposits 
of the above thickness, or containing calcium in amount equal to 
that at present in solution in the ocean, to have accumulated on the 
floor of the ocean. From the data here furnished a' number of other 
interesting speculations might he indulged in, relating to the amount 
of carbonic acid that has been abstracted from the atmosphere and 
fixed in carbonate of lime deposits ; the total amount of disintegra- 
tion of lime-hearing siliceous rocks measured in terms of the calcium 
at present existing in solution in water and fixed in calcareous 
deposits ; the relative proportions of substances secreted from the 
ocean, as compared with other materials derived from the direct 
disintegration of the land, forming deep-sea deposits ; and the 
apparent accumulation of carbonate of lime formations towards the 
equatorial regions of the globe. These various matters will, how- 
ever, be discussed in another place. 
During the course of these investigations at the Scottish Marine 
Station, the following gentlemen have assisted us in carrying on 
the experiments referred to in this communication : — Dr G. S. 
Woodhead, Messrs G. Brook, W. S. Anderson, J. G. Ross, B.Sc., 
G. Young, A. Drysdale, and W. G. Reid. 
APPENDIX. 
Modification of the Method for the Determination of Ammonium Salts 
in Sea Water. 
The method usually followed in water analyses, by which saline 
ammoniacal salts are distinguished from albuminoid nitrogenous 
matter, in so far as the process of distilling the sea water under 
examination, first with pure magnesia to eliminate the ammonia 
actually present, and in the subsequent treatment of the residual 
water with solutions of potash and permanganate of potash, being 
