728 REPORT—1899. 
generally how insuflicient in precision, are the observations on this topic! A few 
rivers have been more or less systematically examined, some widely varying 
results have been obtained from the observations, and while enough has been 
obtained to show the interest and importance of the method of research, no ade- 
quate supply of materials has been gathered for the purposes of accurate deduction 
and generalisation. What we need is a carefully organised series of observations 
carried out on a uniform plan, over a sufficient number of years, not for one river 
only, but for all the important rivers of a country, and indeed for all the greater 
rivers of each continent. We ought to know as accurately as possible the extent 
of the drainage-area of each river, the relations of river-discharge to rainfall and 
to other meteorological as well as topographical conditions; the variation in the 
proportions of mechanical and chemical impurities in the river-water according to 
geological formations, form of the ground, season of the year and climate. ‘The 
whole geological 7égzme of each river should be thorougbly studied. The admi- 
rable report of Messrs. Humphreys and Abbot on the ‘ Physics and Hydraulics of 
the Mississippi,’ published in 1861, might well serve as a model for imitation, 
though these cbservers necessarily occupied themselves with some questions which 
are not specially geological and did not enter into others on which, as geologists, 
we should now gladly have further information. 
Again, the action of Glaciers has still less been subjected to prolonged and 
systematic observation. The few data already obtained are so vague that we 
may be said to be still entirely ignorant of the rate at which glaciers are wearing 
down their channels and contributing to the denudation of the land. 
The whole of this inquiry is eminently suitable for combined research. Each 
stream or glacier, or each well-marked section of one, might become the special 
inquiry of a single observer, who would soon develop a paternal interest in his 
valley and vie with his colleagues of other valleys in the fulness and accuracy of 
his records. 
Nor is our information respecting the operations 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 lifetime, the estimates of the rate of advance 
or retreat of the shore-line are based for the most part on no accurate determina- 
tions. 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 information 
regarding alterations of our coasts, and that with the sanction of the Lords of the 
Admiralty the co-operation of the Coast-guard throughout the three kingdoms has 
been secured. We may therefore hope to be eventually in possession ot trust- 
worthy statistics on this interesting subject. 
The disintegration of the surface of the land by the combined agency of the 
Subaérial 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 
meteorological 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 atmospheric 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 attention 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.1 I would urge upon town-geologists, and those in the country who 
have no opportunities of venturing far afield, that they may do good service by 
careful scrutiny of ancient buildings and monuments. In the churchyards they 
will find much to occupy and interest them, not, however, like Old Mortality, in 
repairing the tombstones, but in tracing the ravages of the weather upon them, 
and in obtaining definite measures of the rate of their decay. 
The conditions under which subaérial disintegration is effected in arid climates, 
and the rate of its advance, are still less known, seeing that most of our informa- 
tion is derived from the chance observations of passing travellers. Yet this branch 
' Proc, Roy. See, Edin, vol. x. (1879-80), p. 518, 
