OcTOBER 13, 1899. ] 
erations of the sea much more precise. Even 
in an island like Great Britain, where the 
waves and tides effect so much change within 
the space of a human life-time, the estimates 
of the rate of advance or retreat of the shore- 
line are based for the most part on no accu- 
rate determinations. It is satisfactory to 
be able to announce that the Council of this 
Association has formed a Committee for the 
purpose of obtaining full and accurate in- 
formation regarding alterations of our 
coasts, and that with the sanction of the 
Lords of the Admiralty, the cooperation of 
the Coast-guard throughout the three king- 
doms has been secured. We may, therefore, 
hope to be eventually in possession of trust- 
worthy statistics on this interesting subject. 
The disintegration of the surface of the 
land by the combined agency of the sub- 
aérial forces of decay is a problem which 
has been much studied, but in regard to 
whose varying rates of advance not much 
has been definitely ascertained. The me- 
teorological conditions under which it takes 
place differ materially according to latitude 
and climate. and doubtless its progress is 
equally variable. An obvious and useful 
source of information in regard to atmos- 
pheric denudations is to be found in the 
decay of the material of buildings of which 
the time of erection is known, and in dated 
tombstones. ‘Twenty years ago I called at- 
tention to the rate at which marble gives 
way in such a moist climate as ours, and 
cited the effects of subaérial waste as these 
can be measured on the monuments of our 
graveyards and cemeteries.* I would urge 
upon town-geologists, and those in the 
country who have no opportunities of ven- 
turing far afield, that they may do good ser- 
vice by careful scrutiny of ancient buildings 
and monuments. In the churchyards they 
will find much to oceupy and interest them, 
not, however, like Old Mortality, in repair- 
ing the tombstones, but in tracing the 
* Proc. Roy. Soc. Edin., Vol. X. (1879-80), p. 518. 
SCIENCE. 525 
ravages of the weather upon them, and in 
obtaining definite measures of the rate of 
their decay. 
The conditions under which subaérial dis- 
integration is effected in arid climates, and 
the rate of its advance, are still less known, 
seeing that most of our information is de- 
-rived from the chance observations of pass- 
ing travelers. Yet this branch of the sub- 
ject is not without importance in relation to 
the denudation, not only of the existing ter- 
restrial surface, but of the lands of former 
periods, for there is evidence of more than 
one arid epoch in geological history. Here, 
again, a diligent examination of ancient 
buildings and monuments might afford 
some, at least, of the required data. In 
such a country as Egypt, for instance, it 
might eventually be possible to determine 
from a large series of observations what has 
been the average rate of surface-disintegra- 
tion of the various kinds of stone employed 
in human constructions that have been 
freely exposed to the air for several thou- 
sand years. 
Closely linked with the question of denu- 
dation is that of the deposition of the mate- 
rial worn away from the surface of the land. 
The total amount of sediment laid down 
must equal the amount of material ab- 
stracted, save in so far as the soluble por- 
tions of that material are retained in solu- 
tion in the sea. But we have still much to 
learn as to the conditions, and especially as 
to the rate, of sedimentation. Nor does 
there appear to be much hope of any con- 
siderable increase to our knowledge until 
the subject is taken up in earnest as one de- 
manding and justifying a prolonged series 
of well-planned and carefully executed ob- 
servations. We have yet to discover the 
different rates of deposit, under the varying 
conditions in which it is carried on in lakes, 
estuaries, andthe sea. What, for instance, 
would be a fair average for the rate at which 
the lakes of each country of Europe are now 
