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The history of the use of railroad ballast is traced in skeleton form, primarily to indicate the reasons for the development of ballast as used today. The functions served by ballast in spreading the load, in decreasing impact stresses, and in draining water away from under the ties are described. Also, the destructive forces, both those of nature and those incident to the use of ballast, are discussed, for these must be resisted and they influence the minimum quality of aggregates which are suitable for use under the track. Efforts made to correlate ballast behavior with laboratory tests are cited and, finally, the essential features of the present American Railway Engineering Association specifications for ballast are given to show the trend in the thinking of engineers regarding the qualities necessary for suitable ballasts.

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