I9I2.] CLARKE— SOME GEOCHEMICAL STATISTICS. 231 



unaccounted for. Part of it goes to form pyrite, and part is decom- 

 posed by organic agencies and lost, but the proportion of loss is 

 unknown. It is, doubtless, large. The potassium which is taken up 

 by clays or else in glauconite is in either instance represented as 

 silicate, and hence a part of the silica is regarded as in combination. 

 The sesquioxides are calculated as limonite, although a part of them 

 is certainly alumina ; but no refinement of a calculation here would 

 change the order of magnitude as given. The several orders of 

 magnitude are probably close to the truth, and we may say with 

 much confidence that the precipitates, including such substances as 

 coral, shell, diatomaceous ooze and what not are formed at a rate 

 of something like 21 X 10^ metric tons a year, plus a small but unde- 

 fined allowance for that part of the sulphur which has been fixed as 

 pyrite. 



At the figure given, chemical sediments are now forming in the 

 ocean sufficient to cover 88,000,000 square miles of the sea floor to 

 the depth of 0.0001337 inch annually. The whole area of the ocean 

 is 139,440,000 square miles, but the portion covered by the red clay, 

 where the precipitation is relatively insignificant, must be deducted. 

 If the rate had been uniform throughout geological time, 83,472,000 

 years these sediments would form a layer about 930 feet deep, but 

 such a calculation is unsound. Large areas of what were once 

 marine sediments are now land, and, moreover, neither the rate nor 

 the distribution of the deposits can have been uniform. The lime- 

 stones that are forming now are largely derived from the solution of 

 older deposits, Cambrian, Silurian, Devonian, Cretaceous, etc., and 

 their carbonates have been deposited in the ocean, not once only, 

 but possibly several times. In the earliest geologic eras, when 

 sediments began to form, the proportion of carbonates to other salts 

 thrown down must have been much smaller than today. An average 

 thickness of 930 feet over the assumed area is therefore a great 

 exaggeration ; and needs to be reduced. 



It is probably impossible to determine, with any approach to 

 precision, the actual quantity of marine sediments that have been 

 formed. We can, however, make a plausible estimate, which shall, 

 at least, give us some conception of their order of magnitude. It has 



