Edinburgh Geological Society. 561 
from a very slow motion is produced in a moment of time. Principal 
Forbes, standing on a point which commanded the whole range of the 
Alps from Turin to the Adriatic, and having the whole vast plain 
of Lombardy at his feet, was thus enabled to see the rush of that 
mighty shadow, and to form some conception of the velocity of cosmic 
motions as measured upon the distances of our earthly surface. The 
sight was, he told me, the most impressive it had ever been his lot to 
witness. But we need not leave the surface of our own globe, or 
compare its magnitudes with the magnitudes of surrounding space, 
to be convinced of the childishness of our language when we apply 
the word catastrophe to movements upon or in the crust of the earth, 
which in reality are movements of extreme minuteness, even as 
measured by the units of magnitude with which we are familiar on 
its surface. I had occasion the other day, in delivering a popular 
lecture in Glasgow, to exhibit a section of the globe drawn on the 
scale of one-tenth of an inch to a mile. On that scale, which I have 
taken from my friend Mr. James Nasmyth, the globe is represented 
by a circle 64 feet in diameter, and I was able to show that on that 
portion of the curve which represents one-eighth of the circumference, 
the elevation of the highest mountain in Europe, Mont Blanc, was 
wholly invisible to the spectators who were half-way down the hall, 
and could hardly be seen even by those who were close at hand. The 
truth is, that when we come to realize the almost infinitesimal small- 
ness of the irregularities of the earth’s surface as compared with its 
circumference, the whole range, from the highest height to the deepest 
deep, being somewhat less than 60,000 feet, the wonder comes to be 
that if subterranean forces are at work at all in modifymg, from 
time to time, the perfect smoothness and sphericity of the surface, not 
that their work should be so great, but that it should be so very small. 
The general result of these considerations is to show, in the first 
place, that the continuity of physical causation is not only consistent, 
but is usually and normally connected with alternations of activity and 
of repose, and that in the periods of activity the results of long- 
continued action are apt to become apparent in effects both sudden 
and extensive. The next result of these considerations is to show 
further, that, as regards any visible effect of subterranean forces upon 
the crust of the earth, there is no so-called ‘‘ catastrophe”? which has 
ever been evoked, even in the most extreme theory, which is not very 
far within the reach and compass of the forces to which they are 
ascribed. I have urged this—as it may appear to many—somewhat 
abstract argument, because, like many other abstract arguments, it 
has a most practical bearing. It seems to me that the dogma or 
doctrine of uniformity, as it has been understood and appled in 
England, has long been exercising a most injurious effect on some 
of the most pressing problems of geological science. I call them the 
most pressing, because they concern the most recent events and 
_ facts. If we cannot interpret, as yet, with any approach to unanimity, 
those changes on the surface of the earth which have taken place most 
recently—even, it may be said, im our own time—as regards the intro- 
duction of our race, how can we attempt to interpret the changes 
which took place in Palaeozoic and Mesozoic times? It may be humbling 
DECADE II.—VOL. X.—NO. XII. 36 
