524 SCIENCE. 
treatment here. But let me illustrate my 
meaning by selecting a few instances where 
the adoption of these more rigid methods of 
inquiry might powerfully assist us in deal- 
ing with the rates of geological processes 
and the value of geological time. Take, for 
example, the wide range of lines of investi- 
gation embraced under the head of denuda- 
tion. So voluminous a series of observa- 
tions has been made in this subject, and so 
ample is the literature devoted to it, that 
no department of geology, it might be 
thought, has been more abundantly and 
successfully explored. Yet if we look 
through the pile of memoirs, articles and 
books, we cannot but be struck with the 
predominant vagueness of their statements, 
and with the general absence of such numer- 
ical data determined by accurate, systematic 
and prolonged measurement as would alone 
furnish a satisfactory basis for computations 
of the rate at which denudation takes 
place. Some instrumental observations of 
the greatest value have indeed been made, 
but, for the most part, observations of this 
kind have been too meagre and desultory. 
A little consideration will show that in 
all branches of the investigation of denuda- 
tion opportunities present themselves on 
every side of testing, by accurate instru- 
mental observation and measurement, the 
rate at which some of the most universal 
processes in the geological régime of our 
globe are carried on. 
It has long been a commonplace of geology 
that the amount of the material removed in 
suspension and solution by rivers, furnishes 
a clue to the rate of denudation of the 
regions drained by the rivers. But how 
unequal in value, and generally how in- 
sufficient 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 impor- 
(N.S. Vou. X. No. 250. 
tance of the method of research, no adequate 
supply of materials has been gathered for 
the purposes of accurate deduction and gen- 
eralization. What we need is a carefully 
organized 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 in- 
deed for all the greater rivers of each con- 
tinent. 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 varia- 
tion in the proportions of mechanical and 
chemical impurities in the river-water ac- 
cording to geological formations, form of 
the ground, season of the year and climate. 
The whole geological régime of each river 
should be thoroughly 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 observers necessarily occupied them- 
selves 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 fullness 
and accuracy of his records. 
Nor is our information respecting the op- 
