96 SECTIONAL ADDRESSES 
but, as we know, they are not regarded as impossible by the school of 
anthropologists, who trace all mankind to one ancestral home. ‘There is, 
of course, another theory, but the controversy is not within the ambit of 
my topic to-day. It may be that the march of our science will yet test 
both hypotheses more thoroughly than is feasible at the present state of 
our knowledge. There is at any rate little question that in the subject 
of these rival views lies the chief interest of modern man in pre-historic 
geography. 
II. 
That constant change is the law of geography, as of life, is an axiom 
which calls for no dramatic flights of fancy into a remote past. Change 
is all around us to-day; and to many lay students of geography the 
visible and superficial changes, as opposed to the vaster geological move- 
ments, in the face of nature have a peculiar attraction of their own. 
Picturesque details are always with us. One of us, for example, may 
have examined the treasures collected by Sir Aurel Stein as evidence that 
vast tracts in Central Asia, which are now no better than sandy deserts 
were, not so very long ago, the home of a rich and cultured people. 
Another may have served in Mesopotamia, and seen how the traditional 
Garden of Eden has been transformed into a malarial waste of marshes. 
A third, staying at home and spending a summer holiday on the South 
coast of our own country, may have reflected that Roman galleys once 
sailed from the beach where he stood across to the Thames through 
waterways which are now the cornfields and hop-gardens of Kent. 
These half-obliterated watercourses are for ever catching the observant 
eye : they abound across the railway line from Amiens to Boulogne, and 
their well-worn pebbles are turned up by the plough in countless English 
denes and combes. 
The agencies of change, however, are tireless rather than picturesque ; 
and their very assiduity makes them the fitting subject of study and 
experiment. Probably the easiest of them all, from the ordinary student’s 
point of view, is the wastage of mountain ranges. Look, for example, 
at a hill such as the Saleve outside Geneva, and no trained eye is needed 
to see how it is steadily slipping into the plain below. A vivid picture 
rises to my memory from another continent. It was one morning, after 
two days of torrential rain, at a hill station in the outer Himalayas. A small 
plateau, on which rested a military cemetery amidst a glade of deodars 
and rhododendron trees, had broken away during the night from the 
rock behind and dropped, as a solid mass, into the valley 1,000 feet 
below. There it lay, with the trees and the tombstones still standing, 
athwart the stream which ran through the valley and which was rapidly 
banking up into a temporary miniature lake. Some houses in the valley 
had been engulfed in the landslide, and several lives lost. By this time 
no doubt the scar on the hillside has healed, and part of the debris— 
disintegrated deodars, graves and ruined homesteads—is helping to build 
up a patch of new rice land somewhere in the Sunderbuns. The incident 
opened my eyes to the evidence everywhere of similar attrition which has 
been going on unremittingly since the mountains came into being ; and 
