Microscopical Petrography

Abstract

To the massive and important series of volumes in which the Report of the Exploration of the Fortieth Parallel has been published the Engineer Department of the United States has just added a sixth which, for general interest and usefulness beyond the area of the Survey, is equal if not superior to any that has preceded it. In the course of this protracted and laborious survey many rocks were encountered to which Mr. Clarence King and his coadjutors felt somewhat at a loss to apply the petrographical nomenclature of Europe. He accordingly sought help from the highest European authority on the subject, Prof. Zirkel, of Leipzig, whom he induced to undertake the task of examining the vast collection of rock-specimens which had gathered during so many years of field-work. Prof. Zirkel accordingly crossed the Atlantic, spent some time in New York with Mr. King and his staff in making a preliminary investigation of the collection, and in learning the geological position of the specimens and the geological structure of the wide region from which they had been obtained. Subsequently a large and typical series of rock-specimens was sent over to Leipzig to be submitted to careful microscopical investigation. No fewer than twenty-five hundred thin sections were prepared and examined under the microscope. The result of Prof. Zirkel's laborious task is now given to the world and most appropriately forms a separate volume of the Report on the Geology of the Fortieth Parallel. Mr. King may be congratulated upon the judgment he has shown in the allocation of his materials. He has enriched his official publications with the most important contribution yet made to the petrography of America.

Microscopical Petrography.

By Ferdinand Zirkel. Being Vol. VI. of the Report of the United States Geological Exploration of the Fortieth Parallel made under the direction of the Engineer Department by Clarence King, Geologist-in-charge. (Washington, 1876.)