In most cases, at least, the lowest member of the upper series will be a different type of rock from the uppermost member of the lower series, hence the frequent occurrence of the discordant cross bedding in sandstone should not deceive even the novice into the assumption of an unconformity. READING REFERENCES TO CHAPTER V The zones of fracture and flow:— C. R. VAN HISE. Principles of North American Precambrian Geology, 16th Ann. Rept. U.S. Geol. Surv., 1895, Pt. I, pp. 581-603. BAILEY WILLIS. Mechanics of Appalachian Structure, 13th Ann. Rept. U.S. Geol. Surv., 1893, Pt. II, pp. 217-253. A. DAUBRÉE. Études Synthétiques de Géologie Expérimentale. Paris, 1879, pp. 306-328, pl. II. W. PRINZ. Quelques remarques générales à propos de l’essai de carte tectonique de la belgique, etc., Bull. Soc. Belge Geol., vol. 18, 1904, p. 143, pl. V. Analysis of folds:— VAN HISE and WILLIS as above; DE MARGERIE et HEIM; Les dislocations de l’écorce terrestre (in French and German languages). Zurich, 1888. Geological maps:— WM. H. HOBBS. The Mapping of the Crystalline Schists, Jour. Geol., vol. 10, 1902, pp. 780-792, 858-890. CHAPTER VI THE ARCHITECTURE OF THE FRACTURED SUPERSTRUCTURE [Illustration: FIG. 36.—A set of master joints developed in shale upon the shores of Cayuga Lake near Ithaca, New York (after U. S. G. S.).] [Illustration: FIG. 37.—Diagram to show how sets of master joints differing in direction by half a right angle may abruptly replace each other.] [Illustration: FIG. 38.—Diagram to show the different combinations of the series composing two double sets of master joints, and in _a_, _a_, _a_ additional disorderly fractures.]