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

26 ENGINEERING PROBLEMS OF PANAMA CANAL. PANAMA FORMATION. The Panama formation is a light-colored well-bedded tuff some- what acid in composition. Locally it contains some argillaceous beds. It outcrops extensively from Miraflores to Panama and in a few other places. The formation is at least 400 feet thick and overlies the Caimi to beds. It seems to be relatively porous, fairly well bedded, somewhat jointed, and of a crumbly or friable nature. It was not difficult to drill or blast and is somewhat too soft for good road metal. TORO LIMESTONE. The Toro ° limestone is sandy and fragmental, being locally a coquina or shell marl. Its type locality is at Toro Point, but similar appearing limestone fringes the Caribbean coast, except where large valleys have caused it to be eroded or covered with alluvium. In places it forms low bluffs or headlands, especially at Toro Point, west of the Gatun Dam, and at the mouth of the Cliagres River. It is the rock from which Fort San Lorenzo was built. Rock from this formation was used as a hearting for the Toro Point Breakwater. It was suitable for such a purpose because of the ease and cheapness with which it was blasted and loaded onto railroad cars for transfer to the near-by breakwater. The soft and easily abraded character of this material prevented its use except as a core or heart. The break- water had to be faced or armored with much harder and tougher rock, an abundance of which was available at Porto Bello. PLEISTOCENE FORMATIONS. The Pleistocene formations consist of (a) swamp deposits, black soil and silt, filling old channels to depths of 325 feet below the present sea level; (&) river gravels up to 10 feet above the present normal river levels; (c) old sea beaches 6 to 10 feet above the present beach level; and ((Z) bars, beaches, and the present river alluvium. All of these deposits have a distinct bearing on the engineering prob- lems of the Isthmus. The deep swamp deposits not only made sur- veys difficult, but added much to the cost of building railroad fills across them. The river gravels were useful for ballasting the road, for local concrete work, and for other purposes. Some of the beaches yielded vast quantities of sand for making concrete. The present river alluvium locally has an agricultural value; and some of the river sediment, deposited as bars and shoals which partly obstructed the Atlantic and Pacific entrances to the canal, had to bo dredged away. a Called Caribbean limestone by the author in reports of Isthmian Canal Commission for 1912 and 1913. See p. 63 and p. 570 of report for 1913.