212 E. Howe — Geology of the Isthmus of Panama. 



Art. XXIY. — The Geology of the Isthmus of Panama ; by 

 Ernest Howe. 



Introduction. 



The first serious effort to investigate the geology of the 

 Isthmus of Panama was made by Kobert T. Hill in 1895.* 

 Although his stay on the isthmus was brief and the survey 

 merely a hurried reconnoissance, the principal features of the 

 geology and physiography were recognized. At the time of 

 his visit little or no work was being done by the French com- 

 pany, few records of borings or soundings were available, and 

 many exposures along recent cuts were already in the grasp of 

 the jungle, so that certain details that escaped Hill remained 

 to be worked out by MM. Bertrand and Ziircherf three years 

 later when they made a report to the New Panama Canal 

 Company. Working under more favorable conditions, these 

 geologists were able to revise certain of Hill's views, and 

 especially his conclusions concerning the igneous rocks. 



In the following pages numerous references are made to the 

 reports of Hill and of Bertrand and Zurcher, from which great 

 assistance has been derived in the course of my own studies of 

 the isthmian geology. 



The field work upon which the present paper is based was 

 carried on during a part of the summer of 1906, and in the 

 following dry season from January to April, 1907, nearly ~S.yg 

 months in all. The work was undertaken for the Isthmian 

 Canal Commission and had to do largely with economic 

 matters ; a brief outline of the geology, however, accompanied 

 the report to the Canal Commission^:, a resume of which has 

 been published in " Economic Geology ".§ 



The purpose of the present paper is to record in more detail 

 certain observations on the geology, and more especially on 

 the stratigraphy, that affect the conclusions reached by Hill 

 and the French geologists. There were unusual opportunities 

 for studying the section across the isthmus because of fresh 

 exposures made by recent excavation along the canal line, and 



* Kobert T. Hill, The Geological History of the Isthmus of Panama and 

 Portions of Costa Rica. Bull. Museum. Comp. Zool., vol. xxviii, No. 5, 

 pp. 149-285. Cambridge, 1898. 



f M. Bertrand and P. Zurcher, Etude Geologique sur l'Isthme de Panama\ 

 Rapport de la Commission. Compagnie Nouvelle du Canal de Panama\ etc. 

 Annexe I, pp. 85-120. Paris, 1899. The page references in the present 

 paper are to a reprint of this report. 



X Ernest Howe, Report on the Geology of the Canal Zone, Annual Rep. 

 Isthmian Canal Commission, 1907. Appendix E, pp. 108-138. 



§ Isthmian Geology and the Panama Canal, Economic Geology, 



vol. ii, pp. 639-658. 1907. 



