526 SCIENCE. 
being silted up? If this rate were ascer- 
tained, and if the amount of material 
already deposited in these basins were de- 
termined, we should be in possession of data 
for estimating not only the probable time 
when the lakes will disappear, but also the 
approximate date at which they came into 
existence. 
But it is not merely in regard to epigene 
changes that further more extended and 
concerted observation is needed. Even 
among subterranean movements there are 
some which might be watched and recorded 
with far more care and continuity than have 
ever been attempted. The researches of 
Professor George Darwin and others have 
shown how constant are the tremors, minute 
but measurable, to which the crust of the 
earth is subject.** Do these phenomena in- 
dicate displacements of the crust, and, if so, 
what in the lapse of a century is their cu- 
mulative effect on the surface of the land? 
More momentous in their consequences 
are the disturbances which traverse moun- 
tain-chains and find their most violent ex- 
pression in shocks of earthquake. The 
effects of such shocks have been studied and 
recorded in many parts of the world, but their 
cause is still little understood. Are the dis- 
turbances due to a continuation of the same 
operation which at first gave birth to the 
mountains? Should they be regarded as 
symptoms of growth or of collapse? Are 
they accompanied with even the slightest 
amount of elevation or depression? We 
cannot tell. But these questions are proba- 
bly susceptible of some more or less definite 
answer. It might be possible, for instance, to 
determine with extreme precision the heights 
above a given datum of various fixed points 
along such a chain as the Alps, and by a 
series of minutely accurate measurements 
to detect any upward or downward devia- 
tion from these heights. It is quite con- 
ceivable that throughout the whole his- 
* Report Brit. Assoc., 1882, p. 95. 
[N.S. Vou. X. No. 250. 
torical period some deviation of this kind 
has been going on, though so slowly, or by 
such slight increments at each period of re- 
newal, as to escape ordinary observation. 
We might thus learn whether, after an 
Alpine earthquake, an appreciable differ- 
ence of level is anywhere discoverable, 
whether the Alps as a great mountain-chain 
are still growing or are now subsiding, and 
we might be able to ascertain the rate of the 
movement. Although changes of this na- 
ture may have been too slight during human 
experience to be ordinarily appreciable, their 
very insignificance seems to me to supply a 
strong reason why they should be sought 
for and carefully measured. They would 
not tell us, indeed, whether a mountain- 
chain was called into being in one gigantic 
convulsion, or was raised at wide intervals 
by successive uplifts, or was slowly elevated 
by one prolonged and continuous move- 
ment. But they might furnish us with 
suggestive information as to the rate at 
which upheaval or depression of the terres- 
trial crust is now going on. 
The. vexed questions of the origin of 
Raised Beaches and Sunk Forests might in 
like manner be elucidated by well-devised 
measurements. It is astonishing upon 
what loose and unreliable evidence the ele- 
vation or depression of coast-lines has often 
been asserted. On shores where proofs of a 
change of level are observable it would not 
be difficult to establish by accurate observa- 
tion whether any such movements are tak- 
ing place now, and, if they are, to deter- 
mine their rate. The old attempts of this 
kind along the coasts of Scandinavia might 
be resumed with far more precision and on 
a much more extended scale. Methods of 
instrumental research have been vastly im- 
proved since the days of Celsius and Lin- 
naeus. Mere eye-observations would not 
supply sufficiently accurate results. When 
the datum-line has been determined with 
rigorous accuracy, the minutest changes of 
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