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

GENERAL GEOLOGY OF CANAL ZONE. 25 CAIMITO FORMATION. The Caimito formation, which overlies the Emperador limestone, consists of three members, as follows: (a) A basal light-gray, soft, argillaceous, or claylike, sandstone, which grades upward into a yellow- ish argillitic sandstone that is bluish gray on fresh fracture; (J) a peculiarly calcareous conglomerate with some fragments of much decayed basic rock, which locally give a bright-green stain to small patches of the formation; (c) a light-colored to yellowish argillaceous sandstone fairly well beddod. The upper argillitic sandstone is the rock that outcrops in theChagres River atBarbacoas, near San Pablo. Beds a, b and c may be seen in the section at Bald Hill, north of Mira- flores. Bed b outcrops extensively at San Pablo and near the site of the proposed wireless telegraph station opposite San Pablo. The formation does not outcrop at all in the Culebra Cut. These rocks are relatively easy to drill and blast, and the weathered product from the more clayey bods of this formation might bo suitable for the manufacture of common brick. GATUN FORMATION. The Gatun formation (figs. 1 and 2) consists of three members, as follows : (a) About 500 + feet of marls and argillites, or clay rocks, and some beds of soft sandstone and conglomerate; this member is bluish gray but locally contains many brown specks, indicating frag- ments of organic material; it is rich in the fossil shells of ancient marine life; (6) mostly fine, soft sandstone, about 100 feet thick, containing a few fossils ; (c) light to creamy gray indurated clay beds. I he formation is extensive and constitutes the foundation on which the Gatun Locks are built. Fortunately, its fineness of grain renders it relatively impervious to ground water. The upper part of the formation weathers into red clay, and except where this is cut by streams, it covers the solid rock to a depth of 10 to 25 feet. It is possible that th© rod clay, tho wcatlierêd surfacö covering that obscures much of the Gatun formation, would bo a good source of material for the manufacture of common brick. This rock has been used extensively for fills on the new line of the Panama Railroad, and in other places. It was convenient and cheap to excavate and load and answered well the uses to which it was put. However, it can not bo used for fills that are subject to the scour of a river or of sea waves, because it abrades and weathers easily. This formation has much engineering significance because the Gatun Locks and Dam rest on it as a foundation. Its strength and adequacy to meet such foundational requirements are discussed under the heading “Founda- tions of the Gatun Dam and Locks” (p. 39).