734 Marvels of the Universe 
Photo by) [i J. ‘Shepstone. 
SAND-DUNES IN THE COLUMBIA VALLEY. 
These waves may sometimes be piled up to a height of five hundred feet. As it is the wind that forms these ridges, so it is 
the wind that furnishes the sand. Wind-action will produce in one hundred years an amount of sand that would take three 
thousand years of water-action. 
have been the case with some pre-Cambrian rocks of Charnwood Forest and the St. Peter Sandstone 
of the Upper Mississippi. 
Moving sands have been responsible for the wrecking of many a wood or forest. A prevailing 
wind will constantly tend to carry the sand from the windward side of a dune over its crest, and 
strew it out on the leeside. This, of course, results in the steady forward movement of the whole 
mass, and in this case it is a veritable moving wave of sand. In the beginning of the last century 
a church in the neighbourhood of the Kurisches Haff was separated from the sea by sand-dunes. 
By 1839 the church was completely covered by the moving dunes, and by 1869 the sand had pro- 
ceeded still further inland and left the ruins of the church exposed. 
Just a word, in conclusion, as to what it is that sand is composed of. Reduced to its simplest 
form it is just silica, or the oxygen of the air combined with silicon. The most familiar forms of 
silica are flint and quartz, and these, in their finely-divided state, give rise to almost all of the waves 
of the desert and the dunes of the seashore. It can be imagined, when this is realized, what a large 
proportion of the earth’s surface is made up of silica. It is, in fact, the most abundant solid 
constituent of our globe. 
SOME ENS DCMS 
BY HAROLD BASTIN. 
Ir the reader will examine apple or hawthorn twigs during the winter months, he will almost 
certainly find some that are thickly encrusted with minute objects which, when examined through 
a lens, resemble tiny brown mussels. These are the shells secreted by a well-known orchard pest 
