1. Geology of the central Western Cordillera, west of Buga and Roldanillo, Colombia;Barrero-Lozano;Publ. Geol. Espec. INGEOMINAS, Bogotá,1979
2. The age of the Cayo Formation, Ecuador;Bristow;Newsl. Statigr.,1976
3. The Eocene basement of the inter-Andean corridor in the Latacunga-Ambato through (Ecuador);Cotecchia;Geol. Appl. Idrogeol.,1969
4. Mapa geológico national de la Republica del Ecuador, 1: 1.000.000;Direccion General de Geologia y Minas,1982