THE ALLTGOBHLACH BURN | 17 
Sometimes a dry windy day follows a heavy rain, 
and the fine deposits of the streamlets are dried until 
they become dust. The wind picks up the dust, 
scatters it over gardens and fields, and piles some of 
it up in corners. 
Now, I have called your attention to these simple 
facts in order that you may realize some of the 
forces that have been at work all over the world for 
ages upon ages, and have been largely responsible 
for making the earth what it is at present. Just 
as streamlets in rainy weather wear away this road, 
carry away its material and deposit it elsewhere, so 
running water in past ages has carried away whole 
land surfaces, and placed their material in lakes 
and seas. Running water has changed the geog- 
raphy of the world over and over again. It has 
removed mountains and thrown them into the sea, 
and its deposits have been raised out of the sea into 
new land surfaces. Frost has been the means of 
breaking up solid granite into small particles, and 
water has carried these particles away. Wind has 
lifted thousands upon thousands of tons of sand, and 
raised it into sandhills. 
I was staying in the island of Arran in August, 
1910. It was the wettest August we have had 
for many years. But the rain did not spoil my 
holiday ; on the reverse, it taught me some very 
enjoyable lessons. On Plate 4I give you a picture 
of the lower portion of the Alltgobhlach Burn, 
which runs its picturesque and musical course down 
a precipitous hillside on the north-west of the island. 
It rises some two thousand feet above sea-level— 
right among some granite hills. In the picture it 
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