APPENDix B.


 A GEOLOGICAL STUDY OF THE ISTHMUS OF PANAMA.
 By Mr. MARCEL BERTRAND,
 Member of the Institute of France; Professor of Geology at the National High School of Mines at Paris, and
 Mr. PHILIPPE ZURCHER,
 Chief Engineer in the Corps of Bridges and Routes of Communications of France. [Translation by Capt. John C. Oakes, U. S. Army.]


 GEOLOGICAL SECTION OF THE ISTHMUS.

 Preliminary work.-The real basis of our knowledge concerning the age of the strata of Panama is to be found in two publications by Mr. Douvill6 (March, 1891, and December, 1898). The first of these notes was based on the examination of a series of fossil specimens collected by Mr. Canelle, late engineer of the canal company. The second, of which only a rsum6 has so far appeared, begins the study of the fossils which were reported by Mr. Znircher.
 We have also used an important treatise by Mr. Hill, published in 1898, giving an account of an expedition to the Isthmus and to Costa Rica in 1895. The fossils collected by Mr. Hill have been determined by Mr. Dall, who gives a greater age to9the region of the Isthmus than Mr. Douvill6; this discrepancy seems to be especially founded on certain misunderstandings as to the assimilation with the European fauna. As to stratification, Mr. Hill had knowledge of only a very small part of the data furnished by the borings at the canal site. These data have led us to modify considerably the conclusions of Mr. Hill concerning the age of the eruptive rocks of the Isthmus.
 We must mention, moreover, the memoir of Mr. Wagner, which contains few valuable conclusions concerning the age of the land or the rocks, but which does furnish some valuable data about the topography and the lay of the strata of the contiguous region. Mr. Wagner is the only geologist whose explorations have extended a considerable distance from the axis of the canal.
 Finally, we have made use of the memoir of Mr. Boutan, which is especially important in studying the eruptive rocks, and the geological description of the surveying commission of 1884. All of these documents have been compared with one another,, and have been completed by a comparison with the shafts and borings which were made by the old aid the new companies. As to the borings of the former company, it should be mentioned that we have not had the collected specimens at our disposal, but we are sure that the criticism .of the ancient geological profile, drawn up at the time of stoppage of the work of the old company, was much exaggerated, and that the designations, although often little conforming with the usual designations, were nevertheless in perfect relation and can therefore be used to advantage. Besides the numerous shafts sunk by the new company along the whole central trench, shafts, the specimens from which were seen on the premises by Mr.- Zrcher and studied by us in Paris, are sufficient, we believe, to assure a considerable certainty to our principal conclusions about the strata.
 The microscopic studies were made at PItcole de Mines, by Mr. Termier, professor of mineralogy, for the rocks, and by Mr. Cayeux, demonstrator of geology, for the Culebra terrain. The fossils, as we have said, were determined by Mr. Douvill6.
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