| ‘NATURE 
273 
THURSDAY, JANUARY 5, 1882 
ON THE GEOLOGICAL IMPORTANCE OF THE 
| TIDES 
i has naturally been a source of much satisfaction to 
4, me that a man as able and eloquent as the Astro- 
nomer-Royal for Ireland should have come forward as an 
exponent of the theory which I have advanced concerning 
the part played by tides in the history of the earth and 
the other planets. I cannot but feel therefore that it may 
seem ungracious on my part to appear as a critic, and to 
ask Mr. Ball to reconsider some of the deductions which 
he has made in his Birmingham lecture (see NATURE, 
vol. xxv. pp. 79, 103). I refer to the geological aspects of 
the theory. The interest of the subject will, I feel sure, 
prove a sufficient excuse for my being thus critical. 
There is I believe a growing feeling amongst geologists 
that the extreme uniformitarian view as to geological 
action requires modification. We find on the one hand 
the physicist demanding of the geologist that he should 
hurry on the rate of action, and on the other hand the 
geologist telling the physicist to moderate his demands, 
A theory, therefore, which receives much support from 
purely astronomical considerations concerning the ob- 
served configurations of planets and satellites, and which 
enables geologists to perceive “ow the rate of geological 
action may have been more rapid in the past, is valuable 
as a means of reconciliation between two apparently 
opposed branches of science. All this has been admir- 
ably insisted on by Mr. Ball, but I think that in the 
revulsion from uniformitarianism he has passed consider- 
ably too far into the ranks of the opposite school. 
Accepting the truth of the tidal mode of evolution of the 
earth and moon, the question at issue is as to what 
portion of the series of changes, since the birth of the 
mocn, falls within the region of geological history. 
In my own paper in discussing this point, I said : 
“There are other consequences of interest to geologists 
which flow from the present hypothesis. As we look at 
the whole series of changes from the remote past, the 
ellipticity of figure of the earth must have been continually 
diminishing, and thus the Polar regions must have been 
ever rising and the equatorial ones falling; but, as the 
ocean always followed these changes, they might quite well 
have left no geological traces. 
“The tides must have been very much more frequent and | 
larger, and accordingly the rate of oceanic denudation 
much accelerated. 
“The more rapid alternation of day and night would 
probably lead to more sudden and violent storms, and the 
increased rotation of the earth would augment the 
violence of the trade winds, which in their turn would 
affect oceanic currents. Thus there would result an 
acceleration of geological action.” ! 
At the time when I wrote this I contemplated the possi- 
bility of the tides having been, in the earliest geological 
times,® perhaps twice or thrice as high as at present, and 
* “Precession of a Viscous Spheroid. &c.,” Phil. Trans. Part 2, 1870, 
P- 532. It would occupy too much space to reproduce the other comments 
on the Geological aspects of the theory. 
of 48 earth’s radii, instead of the present 60, and to a day of about 16 hours. 
A double tide gives a quadruple rate of retardation of the earth’s rotation. 
VOL. xxv.—NO. 636 
I now feel inclined to consider this estimate rather as 
excessive than deficient. But Mr. Ball speaks of tides 
of over 600 feet as having perhaps occurred within geo- 
logical times, and I would now ask him to reconsider the 
probability of this view. 
The older geologists attributed the larger part of denu- 
dation to the action of the sea, but according to the 
modern, and undoubtedly the more correct opinion, the 
denuding action of air and rain, with the aid of rivers 
and their countless affluents, is of far greater importance. 
Mr. Ball does not allude to the probable increase of rain- 
fall, but it would, I conceive, be quite as important as 
the direct tidal action. 
If the ordinarily received theory of the trade and anti- 
trade winds be correct, it follows that in similar planets, 
at equal distances from the sun and with the same depth 
of atmosphere, the velocity of the wind should vary as 
the linear velocity of a point at the planet’s equator. The 
pianet Jupiter rotates 2°4 times as fast as the earth, and 
has a radius 10} times as great ; hence if it were not for 
the greater distance from the sun the trades should blow 
with 25 times the violence which we observe on the earth, 
But solar radiation at Jupiter is about 5} of that at the 
earth. Hence if Jupiter had an atmosphere of the same 
depth as that of the earth, the trade-winds might blow 
with about the same violence. If however there be a 
much deeper atmosphere on that planet, then the amount 
of solar heat absorbed might be much greater, and the 
violence of the winds increased. The bands on Jupiter, 
which are due to the trades and anti-trades, thus afford 
some evidence that the atmosphere of Jupiter is very 
deep. It seems, however, quite possible that the violence 
of the Jovian trades is due partially, or to a great extent, 
to the heat of the Jovian nucleus. 
But now let us return to the case of the earth. The 
table of numerical values which I have computed (Of. czz. 
P. 494) shows that, when the lunar distance was ten earth’s 
radii (which gives Mr. Ball’s tide of 648 feet), the earth 
must have been rotating in about seven hours. Accord- 
ingly it is probable that the trades and anti-trades blew 
with about 3} their present velocity. This violence of 
, the general atmospheric circulation to and from the 
equator, coupled with the rapid alternations of day and 
night, would undoubtedly give rise to vortical storms of 
prodigious violence. 
Now if this state of things existed in geological history 
we should expect to find the earlier sedimentary rocks of 
much coarser grain than the modern ones; but I am not 
aware that this is the case. Again to withstand such 
blasts, the earliest trees should have trunks of enormous 
thickness, and their leaves must have been very tough, 
or they would have been torn to shreds. There seems to 
be no reason to suppose that the trees of the carboni- 
ferous period present marked peculiarities in these 
respects. 
It is on these grounds that I venture to dissent from 
Mr. Ball in the geological interpretation to be placed on 
the tidal theory, and I think we must put these violent 
phenomena in pregeological periods. 
The dispute is, however, only as to the amount of in- 
| fluence, and I cannot learn that geologists are in a posi- 
2 A double tide would (in round numbers) correspond to a lunar distance | 
tion to affirm that in early periods the storms were not 
say twice as frequent, and the tides twice as high. The 
L 
