On the Clay Pebble-Bed of Ancon (Ecuador)

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Abstract
The clay pebble-bed was first noted by one of us (C. B. B.) in 1919. It was further examined, and part of the outcrop mapped by him in 1922, when its nature and origin were realized. Mr. A. J. Ruthven Murray completed the mapping later. The authors of this paper examined the bed again in 1923, when final conclusions as to its mode of origin were reached. The outcrop is limited in extent, covering not more than 2½ square miles; the numerous small areas are separated by tracts of stratified beds. The best exposure is along the sea-cliffs of Ancon Bay, on the south of the Santa Elena Peninsula. This peninsula is at the northern extremity of the Gulf of Guayaquil, 70 miles west of the town of Guayaquil, and some 130 from the main Andean chain. A typical hand-specimen shows polished rounded or subangular pebbles of harder clay embedded in a matrix of softer clay. The ‘clay-pebbles’ vary from the size of a pin's head up to pieces 2 or 3 inches in diameter, and in rare instances the larger ones themselves contain smaller clay-pebbles. They are easily picked out of the matrix, leaving a smooth polished cast covered by a film of iron-staining. Both pebbles and matrix are grey; the films are grey, green, or brown. In the mass, as in cliff-sections, the clay pebble-bed is seen to contain, in addition, big and partly rounded boulders of sandstone, foraminiferal limestone, and pebbly grit, 2 or 3 feet in

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