TRANSACTIONS OF SECTION D. 9 
certain that the tides were not sufficiently higher in Silurian times to prevent the 
deposition of certain beds of great thickness under conditions as tranquil as any of 
which we have evidence in the case of a formation extending over a large area, 
From the character of the organic remains it is known that these beds were laid 
down in the sea, and there are the strongest grounds for believing that they were 
accumulated along shores and in fairly shallow water. The remains of extremely 
delicate organisms are found in immense numbers, and over a very large area, 
The recent discovery, in the Silurian system of America, of trilobites, with their 
long delicate antennz perfectly preserved, proves that in one locality (Rome, New 
York State) the tranquillity of deposition was quite as profound as in any locality 
yet discovered on this side of the Atlantic. 
There are, then, among the older Paleozoic rocks a set of deposits than which 
we can imagine none better calculated to test the force of the tides; and we find 
that they supply evidence for exceptional tranquillity of conditions over a long 
period of time. 
There is other evidence of the permanence, throughout the time during which 
the stratified rocks were deposited, of conditions not very dissimilar from those 
which obtain to-day. Thus the attachments of marine organisms, which are per- 
manently rooted to the bottom or on the shores, did not differ in strength from 
those which we now find—an indication that the strains due to the movements 
of the sea did not greatly differ in the past. 
We have evidence of a somewhat similar kind to prove uniformity in the 
movements of the air. The expanse of the wings of flying organisms certainly 
does not differ in a direction which indicates any greater violence in the atmo- 
spheric conditions. Before the birds had become dominant among the larger 
flying organisms, their place was taken by the flying reptiles, the pterodactyls, 
and before the appearance of these we know that, in Paleeozoic times, the insects 
were of immense size, a dragon-fly from the Carboniferous rocks of France being 
upwards of 2 feet in the expanse of its wings. As one group after another of 
widely dissimilar organisms gained control of the air, each was in turn enabled to 
increase to the size which was best suited to such an environment, but we find that 
the limits which obtain to-day were not widely different in the past. And this is 
evidence for the uniformity in the strains due to wind and storm no less than to 
those due to gravity. Furthermore, the condition of the earth’s surface at present 
shows us how extremely sensitive the flying organism is to an increase in the 
_ former of these strains, when it occurs in proximity to the sea. Thus it is well 
known that an unusually large proportion of the Madeiran beetles are wingless, 
while those which require the power of flight possess it in a stronger degree than 
on continental areas, This evolution in two directions is readily explained by the 
destruction by drowning of the winged individuals of the species which can 
manage to live without the power of flight, and of the less strongly winged indi- 
viduals of those which need it. Species of the latter kind cannot live at all in the 
far more stormy Kerguelen Land, and the whole of the insect fauna is wingless, 
The size and strength of the trunks of fossil trees afford, as Professor George 
Darwin has pointed out, evidence of uniformity in the strains due to the condition 
of the atmosphere. 
We can trace the prints of raindrops at various geological horizons, and in some 
cases found in this country it is even said that the eastern side of the depressions 
is the more deeply pitted, proving that the rain drove from the west, as the great 
majority of our storms do to-day. 
When, therefore, we are accused of uniformitarianism, as if it were an entirely 
unproved assumption, we can at any rate point to a large body of positive evidence 
which supports our contention, and the absence of any evidence against it. 
Furthermore, the data on which we rely are likely to increase largely, as the result 
of future work. 
After this interpolation, chiefly of biological argument in support of the geolo- 
gist, I cannot do better than bring the geological evidence to a close in the words 
which conclude Sir Archibald Geikie’s address: ‘ After careful reflection on the 
subject, I affirm that the geological record furnishes a mass of evidence which no 
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