Some Engineering Problems Of The Panama Canal In Their Relation To Geology And Topography

ROCK MATERIAL USED IN CANAL CONSTRUCTION. 37 on the Canal Zone stand up as ridges or hills. One of these ridges, 2 miles south of New Frijoles, was “spotted” from a railroad train. Then trails were cut to it and a few small strippings made. The rock proved to be basalt, but subsequent work showed that, like nearly all the basalt masses of the Canal Zone, it was much jointed and broke into fairly smal] fragments on blasting. This quality though very desirable in rock to be used for concrete or road work ren- dered the basalt at this place unsuitable for facing a breakwater— the chief purpose for which it was required—unless reinforced by large heavy bowlders. Several other hard-rock areas were examined, but wore all found to be more or less sheared and jointed, so that they would break into pieces too small to bo really suitable for warding off the attacks of soa waves. SOSA HILL. Sosa Hill, close to the Pacific entrance, was found to be a fairly solid mass of andesitic rock, which, had few shear joints and in which the shrinkage joints were far enough apart so that it would largely blast out in pieces weighing some tons with a relatively small per- centage of fine material. This then is the best source known within the Canal Zone of material for armoring against heavy sea waves. However, the andesitic rock from Porto Bello may break out larger and be more economical for this purpose than the product from Sosa Hill. CHAGRES RIVER GRAVEL. The gravel for railway ballast and other purposes was obtained from the Chagres River near Gamboa Bridge. This is practically the only source of gravel within the Canal Zone. The lower Chagres contains too much alluvium, and in the upper part most of the rocks arc too hard and tough and the streams too weak, except in flood time, to furnish much gravel. The availabls deposits lie between the rocky upper and the alluvial lower parts of the river near the railroad bridge, and thus convenient to transportation. The Chagres deposit furnished most of the ballast for the new line of the Panama Railroad. UNSATISFACTORY GRAVEL IN CANAL ZONE STREAMS. The Canal Zone streams as a rule do not yield much good gravel for the following reasons: (1) They are too short and most of them rise in ridges of hard rock, which affords relatively little material that they can easily wear into rounded gravel; (2) except in the flood season most of the streams are too feeble to roll stones along and grind them into rounded gravel; (3) in the wot season, after heavy rains, the streams become raging torrents, which tend to sweep away into the Chagres River or into the ocean, material that might otherwise be a source of gravel;