Joty—On the Radium-Content of Deep-Sea Sediments. 298 
is, on the other hand, comparable with that of many ordinary 
sedimentary rocks. 
An interesting question arising in connexion with these 
measurements is as to the source of the radioactive substances in 
mid-ocean sediments. Are they chemically extracted from a true 
solution in the sea-water, much as are the manganese of the nodules 
and the potash of the glauconite? or, are they derived in whole, or 
in part, from suspended particles? It is almost certain that the 
gteater richness in the more open parts of the ocean is traceable to 
the comparatively small amounts of calcareous materials which 
reach the depths ; there being, on this account, less dilution of the 
radioactive substances. The lime-secreting organisms of the ocean 
appear to possess a power of rejecting to a great degree radioactive 
substances when secreting calcium carbonate. Wemay see this at 
once by considering the fact pointed out by Gustav Bischof in his 
Chemical and Physical Geology,’ that an oyster will require the 
lime from some 27,000 to 76,000 times its weight of sea-water 
in order to secrete its shell. If the radioactive materials were 
secreted along with the lime, the caleareous rocks which are built 
of such calcareous remains would be very much more radioactive 
than experiment shows. Hence it is not remarkable that the 
tests of Foraminifera should act as dilutants of other radioactive 
products collecting at the ocean bottom. But this still leaves 
open the question as to the ultimate source of the radium or 
uranium of the ocean floor. Thus, if these were derived from 
an extra-terrestrial source, associated with meteoric dust, we should 
again find the deeper parts of the ocean, where Red Clay and 
Radiolarian Ooze accumulate with extreme slowness, characterized 
by conspicuous amounts of radium. 
If we may assume that the radioactive substances are being 
laid down at a uniform rate over the Ocean floor, then the 
measurements given above afford an estimate of the relative 
amounts of other substances accumulating in a given time in 
various parts of the Ocean. Thus the deposit of Globigerina Ooze 
collects about eight times as fast as the Radiolarian Ooze or as 
the Red Clay: the two latter collecting at about the same rate. 
It would be a matter of much interest ifthe radium could be 
1 «¢ Blements of Chemical and Physical Geology,’’ vol. i., p. 180, English Trans. 
