ILLUSTRATIONS. Page. PLATE I. Map of part of New England, showing granite centers... II. Map showing locations of Quincy granite quarries.......... 74 90 III. A, Dell Hitchcock quarry, Quincy, Mass.; B, Galvin quarry, Quincy, 96 IV. Ball of polished Quincy granite... 106 V. A, Pigeon Hill Granite Company's Upper quarry, Rockport, Mass.; VI. A, Contact of granite and gneiss, Milford, N. HI.; B, Pegmatite dikes, B, Rockport Granite Company's Deep Pit quarry, near Bay View, VII. A, Granite quarries, Redstone, N. H.; B, Storage yard at Milford, 'FIG. 1. Rift and grain in thin section of Redstone, N. H., granite 2. Horizontal section of diabase dike in Deep Pit quarry, Bay View, 3. Limonitic stain from a crystal of allanite in green granite, Redstone, 4. Hematitic stain in altered Quincy granite..... 5. Granite and gneiss contact at Pease quarry, Milford, N. H. 6. Map showing locations of Milford, Mass., granite quarries.... 7. Structure at Cutting quarry, Milford, Mass...... 8. Structure at East quarry, Milford, Mass... 9. Structure at Reinhalter quarry, West Quincy, Mass.. 11. Structure at Granite Railway quarry, West Quincy, Mass.. 13. Map showing locations of Rockport, Mass., granite quarries. 122 130 131 136 138 140 152 155 21. Map showing locations of Milford, N. II., granite quarries.. 157 22. Structure and plan of Young quarry, Milford, N. H....... 172 23. Map showing locations of Conway, N. H., granite quarries.. 177 4. Map showing locations of Westerly and Niantic, R. I., granite quarries 189 198 26. Diagram of east face of Catto quarry, Westerly, R. I. 199 27. Structure at Klondike quarry, near Niantic, R. I.. 206 6 STANFORSSACHUSETTS, CHIEF COMMERCIAL GRANITES OF By T. NELSON Dale. INTRODUCTION. In Bulletin No. 313, published in October, 1907, by the United States Geological Survey, the granites of Maine were described by the writer from both the scientific and the economic standpoint. The design of the present work is to extend the same method of treatment to the granites of greatest economic importance in Massachusetts, New Hampshire, and Rhode Island. These are the granites of Milford, Quincy, Rockport, and Becket (near Chester) in Massachusetts, of Concord, Milford, and Conway in New Hampshire, and of Westerly in Rhode Island. In addition certain granites from Auburn and Sunapee in New Hampshire are incidentally considered. The granites of Monson and Graniteville, in Massachusetts, and of Troy, in New Hampshire, and of several other places in the three States named, will be taken up in a later publication. Bulletin No. 313 contains a scientific discussion of granite adapted to the general reader, and also, in its economic portion, material of general economic interest. For convenience of reference those parts of that bulletin are here republished, but in revised form. In both bulletins some purely scientific matter necessarily appears in the economic part, in the geological summary which prefaces the description of each group of quarries. The field work upon which this report is based, involving visits to 88 quarries, was done in 1906. The petrographic work necessitated the study of 350 thin sections. The writer is indebted to Dr. Albert Johannsen, of the United States Geological Survey, for critical revision of his determinations of the minerals of these sections, and to Messrs. E. C. Sullivan, George Steiger, and W. T. Schaller, chemists, of the Survey, for determinations of the percentages of lime soluble in hot dilute acetic acid in 23 granites. Miss A. T. Coons, of the Survey, has contributed a chapter of statistics on the granite produced at the centers referred to and in the States named. Prof. Charles Palache, of Harvard University, has consented to the insertion of a note on a dike at Quincy. Mr,.E. W. Branch, C. E., of Quincy, has allowed the reproduction of his. copyrighted map of its quarries. Information as to the general geological relations of the various granites has been obtained from works on local geology by Emerson and Perry, Shaler and Tarr, Sears, Crosby, C. H. Hitchcock, Kemp, and Rice and Gregory. These are quoted or referred to in the section preceding the descriptions of the quarries of each district. The Rosiwal method of estimating mineral percentages has been applied to all the types of granite described. These types will be found defined and classified, both scientifically and commercially, in the table on pages 211-212, which is followed by a section on their relative commercial values. The numbers of the specimens described, to which those of the thin sections correspond, are given, so that the descriptions can be verified by consulting the collections at the National Museum. All these specimens have been prepared from blocks selected by the foremen or superintendents. Such scientific terms as have unavoidably been used are explained in the glossary at the end, where also some of the quarrymen's terms are made intelligible to the general or scientific reader. The names applied to the various granites in this report are, with a few exceptions, merely local or trade designations. Their employment in this economic bulletin does not affect the standing of any particular name as a geologic formation name. PART I.-SCIENTIFIC DISCUSSION. GENERAL FEATURES. GRANITE PROPER. DEFINITION. Granite, in a general sense, is essentially an entirely crystalline igneous rock, consisting mainly of quartz, potash feldspar, and a feldspar containing both soda and lime, also of a small amount of either white or black mica or both, and sometimes of hornblende, more rarely of augite, or both. Where granite has, subsequent to its crystallization, been subjected to pressure sufficient to produce a parallelism in the arrangement of its minerals—that is, a schistosity-it is no longer a true granite, but a gneiss or granite gneiss; a sedimentary rock, however, in becoming crystalline may resemble a granite gneiss and is called a sedimentary gneiss. ORIGIN. Granite is now regarded as the product of the slow cooling and crystallization of molten glasslike matter at a dull-red heat-matter which contained superheated water, and was intruded from below into an overlying mass of rock of sufficient thickness not only to prevent its rapid cooling and its general extrusion at the surface, but also to resist its pressure by its own cohesion and powerfully to compress it by its own gravity. As carbonic acid can be liquefied only under pressure, its presence in liquid form within some of the microscopic cavities in the quartz of granite is alone evidence that the rock was formed under pressure. That the temperature at which granite solidified was comparatively low has been inferred from the fact that it contains minerals which lose their physical properties at temperatures higher than dull-red heat. The relations of the mineral constituents of granite to one another show the order in which they must have crystallized. This order differs from that in which they would crystallize if molten in a dry state, but laboratory experiments have shown that the presence of even a small quantity of water suffices to change that order of crystallization. The presence of superheated water in the formation of granite, inferred from the arrangement of its minerals, and the pressure indicated from a study of the contents of the microscopic cavities of its quartz show that the conditions requisite to its formation included not only the pressure of a great overlying mass of rock but also powerful expansive pressure from below. Had this molten matter been extruded at the surface it would have cooled so rapidly that but few of its constituent molecules would have had time to arrange themselves in geometric order. The process of crystallization would have been arrested by the sudden passage of the material into the solid state and the product would have been a volcanic glass somewhat resembling that which forms cliffs in Yellowstone National Park. In granite, however, the mass has cooled slowly enough to permit the complete crystallization of the originally molten glasslike matter, and no unarranged molecules remain, The overlying rock mass which furnished so large a part of the pressure required to form granite has at many places been removed from it by erosive processes that operated through great stretches of time. Indeed, it is only by the removal of this mass that granite is anywhere naturally exposed. Although this mass may have measured thousands of feet in thickness, its former presence is at some places attested only by a thin capping on the granite or by fragments which the lacerating action of the intruding granite has incorporated into itself. The lacerating effect of an intrusive eruption and the subsequent erosion of some of the overlying strata have been reproduced experimentally. The conversion of granite itself back into a material which upon cooling under ordinary conditions has proved to be a glass, has been effected in the laboratory, and the chief mineral constituents of granite have been artificially crystallized at high temperature in the presence of water vapor under high pressure, but the conditions requisite for the production of a granitic rock from its chemical constituents have not yet been successfully imitated. Some granite shows locally a certain alignment of its mica plates and feldspars, due to the flow of the mass while it was in a plastic state-a structure which was probably controlled by the pressure and form of the bordering rock. This "flow structure" should not be confounded with the schistosity which is due to later pressure and which also involves mineral changes and is usually regional rather than local in extent. The great differences in the grade of texture in granites-the mineral particles ranging from an average diameter of one-fiftieth inch a Howe, Ernest, Twenty-first Ann. Rept. U. S. Geol. Survey, pt. 3, pp. 294-296, Pl. XLIII. Reyer, of the Austrian Geological Survey, has illustrated a granite intrusion by this simple experiment: Upon a table a frame of clay, say 2 inches thick, is constructed about a square piece of board 1 inch thick. After removing the board a mixture of medium thick plaster and red coloring matter is poured into the inclosure. The surface of the red plaster is then sprinkled with a layer of white plaster powder. After making a lens-shaped perforation in the center of the board it is again fitted into the frame and pressed against the red and white layers until the white plaster exudes through the opening, and afterwards the red intrudes the white. The materials are allowed to harden and are then sawn to show the structure. See Reyer, Ed.. Tektonik der Granit Ergüsse von Neudeck und Carlsbad, etc. Jahrb. K.-k. geol. Reichsanstalt, vol. 29, 1879, pp. 432-433, fig. 6. |