The effect of glaciers may be seen in part and their tremendous influence imagined, by the presence of the countless numbers of striated boulders, pieces of rock and pebbles, which are strewn all over our prairies hundreds of miles from any mountains which could have been their home.
It is not necessary to witness the devastation of a cyclone in order to study the effects of wind action. The piling of sand on the sea-shore, the drifting of snow or the whirling of dust in the street illustrate this. The observer may notice where the dust blown from the street has choked and buried the grasses and weeds beside it, and imagine what might be the fate of forests in the path of encroaching sand-dunes.
Sand-Dune on the Shore of Lake Michigan.
Pupils may be told of the dunes which travel great distances: that one way by which this is known is by noting trees and houses that were once back of the traveling sand-hills and are now in front of them; also tell of the sites of ancient cities long buried and now being excavated and brought to light again.
IMPORTANCE OF LEARNING TO INTERPRET PICTURES AS AN AID TO IMAGING THE CONTINENT.
The ability to image the continent or any part of it, from the reading of pictures, is of great importance. It is an inexpressible aid to the imagination in the study of areas that lie outside of the sense grasp. Good pictures should be chosen: pictures showing several different views of the same section of a country; pictures that are a truthful representation of both detail and generalities. (Many wood cuts are as good as photographs for this purpose. Great care, however, should be taken that they are faithful transcripts.)
After a close study of them, questions may be asked the pupil as to climate, structure, nature of rock and soil; whether it may be supposed to be an arid or fertile region; whether the river basins are young or old; what agents were most active in shaping its features, and what its probable destiny: or the pupil may be led to give his own inferences as to conditions, without direct questioning.
In this way contrasting sections of country may be studied and compared, thus making the mental picture more vivid and complete.