[133]. We may mention here, for example, the work in mineralogy of Penfield, noticed in the accompanying chapter on mineralogy. In addition to the accurate determination of the composition and constants of many minerals, some of which have importance from the petrographic standpoint, we owe to him more than anyone the recognition of fluorine and hydroxyl in a variety of species, and thereby the perception of their pneumatolytic origin. His papers have been published almost entirely in the Journal.
[134]. Wright, Methods of Petrographic-Microscopic Research, Carnegie Inst., Washington, 1911, and various papers; many in the Journal.
[135]. Conf. Wright’s work quoted above and the various manuals previously mentioned.
[136]. Kemp, Hand-book of Rocks, 3d ed., New York, 1904. Pirsson, Rocks and Rock-Minerals, New York, 1910.
[137]. Williams, G. H., U. S. Geol. Surv., Bull. 62, Washington, 1890.
[138]. Van Hise, Treatise on Metamorphism, U. S. Geol. Surv., Monograph 17.
[139]. F. W. Clarke, U. S. Geol. Surv., Bull. 591, 1915.
[140]. Hillebrand, Analysis of Silicate and Carbonate Rocks, U. S. Geol. Surv., Bull. 422, 1910.
[141]. Washington, Chemical Analysis of Rocks, pp. 200, New York, 1910.
[142]. Id., Chemical Analyses of Igneous Rocks (1884–1900), U. S. Geol. Surv., Prof. Paper, No. 14, 1903.