> 
—s « 
TRANSACTIONS OF SECTION. D. 817 
arguments drawn from other departments of Nature can explain away, and which, 
it seems to me, cannot be satisfactorily interpreted save with an allowance of time 
much beyond the narrow limits which recent physical speculation would concede.’ 
In his letter to Professor Perry,! Lord Kelvin says :— 
‘So far as underground heat alone is concerned, you are quite right that my 
estimate was 100 million, and please remark * that that is all Geikie wants; but I 
should be exceedingly frightened to meet him now with only twenty million in 
my mouth.’ 
We have seen, however, that Geikie considered the rate of sedimentation to 
be, on the whole, uniform with that which now obtains, and this would demand 
a period of nearly 400 million years. He points out, furthermore, that the time 
must be greatly increased on account of the breaks and interruptions which occur 
in the series, so that we shall probably get as near an estimate as is possible from 
the data which are available by taking 450 million as the time during which the 
stratified rocks were formed. 
Before leaving this part of the subject, I cannot refrain from suggesting a line 
of inquiry which may very possibly furnish important data for checking the 
estimates at present formed by geologists, and which, if the mechanical difficulties 
can be overcome, is certain to lead to results of the greatest interest and importance. 
Ever since the epoch-making voyage of the ‘Challenger,’ it has been known that 
the floor of the deep oceans outside the shallow shelf which fringes the continental 
areas is covered by a peculiar deposit formed entirely of meteoric and volcanic 
dust, the waste of floating pumice, and the hard parts of animals living in the 
ocean, Of these latter only the most resistant can escape the powerful solvent 
agencies. Many observations prove that the accumulation of this deposit is 
extremely slow. One indication of this is especially convincing: the teeth of sharks 
and the most resistant part of the skeleton—the ear- bones—of whales are so thickly 
spread over the surface that they are continually brought up in the dredge, while 
sometimes a single haul will yield a large number of them. Imagine the count- 
less generations of sharks and whales which must have succeeded each other in 
order that these insignificant portions of them should be so thickly spread over 
that vast area which forms the ocean floor! We have no reason to suppose that 
sharks and whales die more frequently in the deep ocean than in the shallow 
fringing seas; in fact, many observations point in the opposite direction, for 
wounded and dying whales often enter shallow creeks and inlets, and not uncom- 
monly become stranded. And yet these remains of sharks and whales, although 
well known in the stratified rocks which were laid down in comparatively shallow 
water and near coasts, are only found in certain beds, and then in far less abun- 
dance than in the oceanic deposit. We can only explain this difference by supposing 
that the latter accumulate with such almost infinite slowness as compared with 
the continental deposits that these remains form an important and conspicuous 
constituent of the one, while they are merely found here and there when looked 
for embedded in the other. The rate of accumulation of all other constituents is 
so slow as to leave a layer of teeth and ear-bones uncovered, or covered by so thin 
a deposit that the dredge can collect them freely. Dr. John Murray calculates 
that only a few inches of this deposit have accumulated since the Tertiary period. 
These most interesting facts prove, furthermore, that the great ocean basins and 
continental areas have occupied the same relative positions since the formation of the 
first stratified rocks ; for no oceanic deposits are found anywhere in the latter. We 
know the sources of the oceanic deposit, and it might be possible to form an esti- 
mate, within wide limits, of its rate of accumulation. If it were possible to 
ascertain its thickness by means of a boring, some conclusions as to the time which 
has elapsed during the lifetime of certain species—perhaps even the lifetime of the 
oceans themselves—might be arrived at. Lower down the remains of earlier 
species would probably be found. The depth of this deposit and its character at 
deeper levels are questions of overwhelming interest; and perhaps even more so is 
1 Nature, Jan. 3, 1895. 2? P. L. and A,, vol. ii. p. 87. 
