Cxi PROCEEDINGS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
portant, though silent, work which our Museum is doing as a popular 
educator. This is work, too, which is not for the hour or the day, but 
which we trust will endure even after our Society has ceased to exist, 
and after those who have founded it have passed away. It has now 
become one of the firmly established institutions of the town and of 
the county. One of the most encouraging features of its success is 
the large number of school children who visit it, particularly on 
Saturday afternoons. 
Speaking of the Museum brings me to what I had intended to say 
regarding our retiring President. It would be presumption on my 
part to enlarge on the services which Dr. Buchanan White has 
rendered to the Perthshire Society of Natural Science, as these 
are already so well known, not only to all the members, but to all 
the citizens of Perth. Suffice it to say that he helped to found it 
a quarter of a century ago, and that ever since he has devoted to 
its interests a large share of his time, his energies, and his wide 
scientific knowledge, and has used his influence and his powers 
of persuasion to induce others to taste for themselves the joys of the 
study of Nature. Such services as these are certainly far beyond the 
reach of any recognition in a tangible form that we could offer. Yet 
I think there is one way in which we could show our gratitude. 
When our Museum was built, the necessary funds were raised as a 
memorial to the late Sir Thomas Moncreiffe. Why should we not 
raise a Testimonial Fund to our retiring President, to be devoted to 
the scheme of Museum Extension which he has so much at heart ? 
Passing from these general remarks on the present position and 
future prospects of our Society, I come now to the subject on which 
I propose to address you very briefly this evening, namely, Denu¬ 
dation, or the gradual wearing down of the Earth’s surface. I have 
chosen this subject because it is the very key-note of all geological 
science. It is the a. b. c., as it were, whereby all geological pheno¬ 
mena must be interpreted. Geologists tell us that the great majority 
of the rocks comprising the earth’s surface have been built up of the 
ruins of older rocks. They tell us that these have been piled up, 
layer upon layer, through countless ages of time, to thicknesses of 
hundreds and thousands of feet. Nay, they even point to an example 
in America,—that continent of all things large,—where, in the Grand 
Canon of the Colorado, we may behold a cleft cut through a vertical 
mile of horizontal sedimentary strata. Now, it is easy to tell us 
that these strata, a mile in thickness, have been built up of grains of 
sand washed down from the sides of primeval mountains. It may 
even be easy to believe the statement on the faith that those who 
make it ought to know. But the question is, can we realise it ? Can 
we, individually, grasp the fact that such stupendous ruin and such 
stupendous re-building have been wrought on the face of the earth, 
not, as was once conveniently supposed, by convulsions and forces 
proportionately vast, but simply by the imperceptibly slow action of 
the forces which are at work around us at the present day ? I confess 
that it was long after I began my geological studies before I saw 
clearly how these things could be, and still more difficult do I find it 
