EARTH SCIENCES LIBR/.3JT GIFT OF REPOKT ON BRITISH PETEOGEAPHIC NOMENCLATIVE by the Joint Committee appointed by the Geological Society of London and the Mineralogical Society 1 [Reprinted from the Mhieraloyical Mayazine Vol. XIX, No. 92, pp. 187-147.] LONDON 1921 MINERALOGICAL SOCIETY Officers and Council for 1920-21. PRESIDENT. Sir WILLIAM P. BEALE, Bart., K.C., F.G.S., F.C.S. PAST-PRESIDENTS. Rev. Prof. T. G. BONNEY, Sc.D., LL.D., F.R.S. (1883-1885). Sir HENRY A. MIERS, M.A., D.Sc., F.RS. (1904-1909). Prof. W. J. LEWIS, M.A., F.R.S. (1909-19,12). A. E. H. TUTTON, M.A., D.Sc., F.R.S. (1912-1915). W. BARLOW, F.R.S. (1915-1918). VICE-PRESIDENTS. Prof. H. L. BOWMAN, M. A., D.Sc., F.G.S. A. HUTCHINSON, O.B.E., M.A., Ph.D., F.G.S. TREASURES. J. W. EVANS, LL.B., D.Sc., F.R.S., Imperial College of Science and Technology, South Kensington, London, S. W. 7. GENERAL SECRETARY. G. T. PRIOR, M.A., D.Sc., F.R.S., Natural History Museum, South Kensington, London, S. W. 7. FOREIGN SECRETARY. Prof. W. W. WATTS, LL.D., Sc.D., F.R.S., Imperial College of Science and Technology, South Kensington, London, S W. 1. EDITOR OF THE JOURNAL. L. J. SPENCER, M.A., Sc.D., F.G.S , Natural History Museum, South Kensington, London, S. W. 7. TRUSTEES. F. N. ASHCROFT, M.A., F.G.S., Sir HENRY A. MIERS, M.A., D.Sc., F.C.S. F.R.S. ORDINARY MEMBERS OF COUNCIL. T. V. BARKER, M.A., B.Sc., F.C.S. Prof. C. G. CULLIS, D.Sc., F.G.S. A. F. HALLIMOND, M.A., F.G.S. F. H. HATCH, O.B.E., Ph.D., F.G.S. A. HOLMES, D.Sc., F.G.S. J. A. HOWE, O.B.E., B.Sc., F.G.S. Miss M. W. PORTER, B.Sc. R. H. RASTALL, MJL, Sc.D., F.G.S. W. A. RICHARDSON, M.Sc., F.G.S. ALEX. SCOTT, M.A., D Sc. W. CAMPBELL SMITH, M.C., M.A., F.G.S. Sir JETHRO J. H. TEALL, M.A., D.Sc., LL.D., F.RS. LIBRARIAN. Prof. W. J. LEWIS, M.A., F.R.S., The New Museums, Cambridge (to which address all publications intended for the Library of the Society should be forwarded). REPORT ON BEITISH PETKOGKAPHIC NOMENCLATIVE by the Joint Committee u appointed by the Geological Society of London and the Mineraiogical Society [Reprinted from the MlncraJof/lcal Magazine, March, Vol. XIX, No. 92, pp. 137-147.] LONDON 1921 MINERALOGICAL SOCIETY Officers and Council for 1920-21. PRESIDENT. Sir WILLIAM P. BEALE, Bart., K.C., F.G.S., F.C.S. PAST-PR ESIDENTS. Rev. Prof. T. G. BONNEY, Sc.D., LL.D., F.K.S. (1883-1885). Sir HENRY A. MIERS, M. A., D.Sc., F.R.S. (1904-1909). Prof. W. J. LEWIS, M.A., F.R.S. (1909-1912). A. E. H. TUTTON, M.A., D.Sc., F.R.S. (1912-1915). W. BARLOW, F.R.S. (1915-1918). VICE-PRESIDENTS. Prof. H. L. BOWMAN, M.A., D.Sc., F.G.S. A. HUTCHINSON, O.B.E., M.A., Ph.D., F.G.S. TREASURER. J. W. EVANS, LL.B., D.Sc., F.R.S., Imperial College of Science and Technology, South Kensington, London, S. W. 7. GENERAL SECRETARY. G. T. PRIOR, M.A., D.Sc., F.R.S., Natural History Museum, South Kensington, London, S. W. 7. FOREIGN SECRETARY. Prof. W. W. WATTS, LL.D., Sc.D., F.R.S., Imperial College of Science and Technology, South Kensington, London, S W. 7. EDITOR OF THE JOURNAL. L. J. SPENCER, M.A., Sc.D., F.G.S , Natural History Museum, South Kensington, London, S. W. 7. TRUSTEES. F. N. ASHCROFT, M.A., F.G.S., Sir HENRY A. MIERS, M.A., D.Sc., F.C.S. F.R.S. ORDINARY MEMBERS OF COUNCIL. T, tf. ^A^KER, M.A., B.Sc., F.C.S. Prof. C. G. CULLIS, D.Sc., F.G.S. A. F. HALLIMOND, M.A., F.G.S. F. H. HATCH, O.B.E., Ph.D., F.G.S. A. HOLMES, D.Sc., F.G.S. J. A. HOWE, O.B.E., B.Sc., F.G.S. Miss M. W. PORTER, B.Sc. R. H. RASTALL, M.A., Sc.D., F.G.S. W. A. RICHARDSON, M.Sc., F.G.S. ALEX. SCOTT, M.A., D.Sc. W. CAMPBELL SMITH, M.C., M.A., F.G.S. Sir JETHRO J. H. TEALL, M.A., D.Sc., LL.D., F.R.S. LIBRARIAN. Prof. W. J. LEWIS, M.A., F.R.S., The New Museums, Cambridge (to which address all publications intended for the Library of the Society should be forwarded). 137 EARTH SCIENCES LIBRARY ' ' ' - **' " '> -." Report of the Committee on British Petrographic Nomenclature. THE Joint Committee was appointed in February 1920, by the Geological Society of London and the Mineral ogical Society : ( To consider whether any standardization of British petrographic nomenclature is possible and desirable, and, if so. to make recommendations with that end in view.' The Committee is composed of the following : Professor W. W. Watts (Chairman), Dr. J. V. Elsden, Dr. J. S. Flett, Sir Jethro J. H. Teall, Dr. Herbert H. Thomas, Mr. G. W. Tyrrell, appointed by the Geo- logical Society of London. Dr. J. W. Evans, Dr. F. H. Hatch, Dr. A. Holmes, Dr. G. T. Prior, Mr. R. H. Rastall, and Mr. W. Campbell Smith (Hon. Sec.), appointed by the Mineralogical Society. The first meeting was held on March 16, and thirteen meetings in all have been held. The average number of members attending has been 7'5. Dr. Flett and Mr. Tyrrell were unable to be present at the meet- ings, but they communicated their views in writing from time to time. After each meeting all members of the Committee received a full report of all recommendations agreed upon. The first two meetings were occupied with a discussion of the resolu- tions which were passed by the Commission of Rock Nomenclature of 1899-1900, set up by the International Geological Congress. The committee then proceeded to consider a list of ninety rock-names and petrographic terms which have been used in more than one sense by British authors. The recommendations of the Committee on the future use of these terms are embodied in the two Lists A and B which follow. List A includes all the terms that were discussed, with the definitions recommended for those terms which the Committee proposed should be retained in use. List B includes twenty-seven names of which the Committee recom- mends the complete rejection. The only obsolete name re-introduced is trachybasalt, which is proposed in place of trachydolerite as used by Washington in 1897. No new names are proposed. Attention is called to the fact that in these lists no names have been dealt with other than those which have been used in more than one sense by British authors. 414164 iSl *"* REPORT OF COMMITTEE ON Adamellite should be discarded. See List B. If some authors wish to retain the term it should be used only in the sense in which it was re- defined by Brogger ; i. e. for the acid member of his ' monzonite series '. Amphibolite is retained 'for unfoliated or slightly foliated meta- morphic rocks of doubtful, or other than igneous, origin. It is composed essentially of hornblende and felspar, often containing various accessories, such as epidote and garnet. Epidiorite is retained for unfoliated metamorphosed igneous rocks of doleritic or basaltic composition in which augite has been replaced by hornblende. It usually occurs as dykes and sills. Hornblende-schist is distinguished from amphibolite and epi- diorite by the possession of foliated texture. Anamesite. Disuse recommended. See List B. Anorthosite is retained in the sense of rocks similar in texture to the gabbros and composed almost entirely of basic plagioclase and almost free from ferromagnesian materials. Aphanite. Disuse recommended. See List B. Aplite and Pegmatite, when used alone as rock-names, should be used in the sense defined in Harker's Petrology for Students, 1919, pp. 38 and 39, as follows : Aplite 'occurs as veins in granite. ... It is a fine-textured rock with "panidiomorphic" to granulitic structure, and is somewhat more acid than the associated granite. A characteristic type occurs in connection with the muscovite-granites near Dublin. It consists of microcline, with some oligoclase, quartz, muscovite, and red garnet.' Pegmatites ' consist essentially of microcline or orthoclase and quartz, often with white mica and sometimes red garnet. The texture is often extremely coarse, and there is a frequent tendency to the graphic structure.' The possession of graphic structure by a pegmatite is not essential. These terms (aplite and pegmatite) may be extended to rocks bearing the same relation to syenite, diorite, &c., as aplite and pegmatite bear to granite, but, if so used, some indication of their mineralogical composi- tion should be given. Banatite. Should be replaced by quartz-diorite (Banat type). Basalt. The term ' basalt ' used alone should not imply the presence of olivine. Basalts containing olivine as an essential constituent should be described as olivine-basalts. No definite line is drawn between basalt and dolerite. The distinction depends on coarseness of texture. Basanite. See note under nephelinite. Bauxitite. Disuse recommended. See List B. BRITISH PETKOGRAPHIC NOMENCLATURE. 139 Binary granite. Disuse recommended. See List B. Bostonite. See note tinder trachyte. Charnockite. The committee recommends that when reference is made to the charnockite series the word ' series ' be never omitted. Reference to this series of rocks as ' the charnockites ' is to be avoided. It is further recommended that charnockite as a rock-name be restricted to the granulitic variety of hypersthene-granite of the type locality as denned by Holland in 1893, and to rocks practically identical with this. Cipolin. Disuse recommended. See List B. Cipollino may be retained for the ornamental stones so named. Comendite should be replaced by soda-rhyolite (Comende type). Cormibianite. Disuse recommended. See List B. Diabase. Disuse recommended. See List B. Diallagite, Disuse recommended. See List B. Diorite should be limited to plutonic rocks of intermediate composi- tion, the dominant felspar being an acid plagioclase. More basic rocks consisting of hornblende and basic plagioclase should be classed with the gabbros. Diorite-aplite. See aplite. Ditroite should be replaced by nepheline-syenite (Ditro type). Dolerite is retained in the sense of a coarse-grained rock of basaltic composition, usually, but not always, hypabyssal. No definite line is drawn between basalt and dolerite. The distinction depends on coarse- ness of texture. Domite. Disuse recommended. See List B. Dunstone. Disuse recommended. See List B. Epi- as a prefix should not be used, but the term epidiorite, being well established, may be retained in use with the definition given above. See under amphibolite. Epidiorite. See under amphibolite. Essexite is retained for rocks practically identical with, or which show but slight divergence from, the original type of Salem Neck, Essex Co., Massachusetts. Euphotide. Disuse recommended. See List B. Eurite. Disuse recommended. See List B. Felsite is retained for those acid and intermediate intrusives which carry no porphyritic constituent and in which the texture is felsitic. Felsitic may be used to designate the cryptocrystalline texture of felsites and similar rocks. The term ' microfelsitic', used by certain authors, is unnecessary. M 2 140 REPORT OF COMMITTEE ON Felspar-rock. Disuse recommended. See List B. Foyaite should be replaced by nepheline-syenite (Foya type). Gabbro includes plutonic rocks of basic composition consisting essen- tially of a basic plagioclase with one or more ferromagnesian constituents, usually a pyroxene but sometimes hornblende, and with or without olivine. See diorite. Gneiss is a medium or coarse-grained crystalline rock possessing some form of parallel structure due either to the uniform orientation of certain tabular or prismatic minerals, or to the presence of wavy dis- continuous surfaces indicating a lenticular or phacoidal structure, or of bands of varying mineralogical composition which retain their continuity and parallelism throughout a considerable mass of rock (banded gneisses). Gneisses may be of igneous, sedimentary, or doubtful origin. Those of igneous origin (orthogneisses) may have acquired their characteristic structure before, during, or subsequent to consolidation, and only in the last-mentioned class can they be said to be metamorphic rocks. Those of sedimentary origin (paragneisses) are invariably metamorphic rocks owing to the development in them of new minerals ; their parallel struc- ture may in some cases follow planes due to deposition, in others due to deformation. The term gneiss, when used without qualification, should imply a rock of granitic composition but not necessarily of igneous origin. Schist (Crystalline schists) differs from gneiss in being of finer grain, and in possessing a well-marked tendency to split into thin layers, except when puckered or folded by movement subsequent to the development of schistosity. The term carries with it no mineralogical connotation. Granite-porphyry. See under porphyry. Granitite. Disuse recommended. See List B. Granodiorite is to be retained for rocks intermediate between quartz- diorite and granite in which orthoclase, while present as a notable con- stituent, is always subordinate in amount to the plagioclase. Granophyre is retained in the sense in which the term is used by Eosenbusch (1872), and by Harker. Granulite is not to be used in the sense of Michel Levy, for muscovite- granite. When used as a rock-name it should be used only for rocks with granulitic texture, and should be qualified by prefixing the name of the mineral, or minerals, which characterize the rock. Granulitic texture may be used for that texture of rocks characterized by even-sized and closely-fitting grains. It is applicable to metamorphosed BRITISH PETKOGRAPHIC NOMENCLATURE. 141 sedimentary and metamorphosed igneous rocks, and, to a more limited extent, to igneous rocks in which the texture has been produced directly. The texture shown in PI. 46, fig. 1, of Mem. Geol. Surv. Gt. Brit., 1907, N.W. Highlands of Scotland, is granulitic. The term granulitic should not be used to describe those textures of dolerites so described by Judd (Q. J. G. S., 1886, vol. 42, pp. 68, 76 and pi. 5). For such textures granulitic should be replaced by intergranular (Evans). Hornblende-schist. See under amphibolite. Hyperite. Disuse recommended. See List B. Hypersthenite. Disuse recommended. See List B. Intergranular. See under granulitic. Kenyte is retained for rocks practically identical with the kenytes of Mt. Kenya described by Gregory, 1900. Keratophyre. See note under trachyte. Lamprbphyre is to be retained in its present generally accepted sense to cover the ' Lamprophyrische Ganggesteine' of Rosenbusch, 1910; i. e. the sense employed by Harker, Petrology for Students, 1919. Leptynolite. Disuse recommended. See List B. Leucite-basalt. See note under nephelinite. Leucite-phonolite is to be used in the sense adopted by Zirkel (1893) for a phonolite containing leucite in addition to nepheline and alkali-felspar. Leucite-trachyte is to be used in the sense of vom Rath (1867), as adopted by Zirkel (1893) and by Washington (1897) ; i. e. a volcanic rock containing leucite in addition to the constituents of trachyte, and consisting, therefore, essentially of alkali-felspar and leucite, with rela- tively small amounts of ferromagnesian minerals, nepheline being absent or present as a minor accessory. Leucitite. See under nephelinite. Leucitophyre. Disuse recommended. See List B. Leuco- should not be used as a prefix indicating the presence of leucite, e.g. in leucoteplirite. Leucotephrite. Disuse recommended. See List B. Melaphyre. Disuse recommended. See List B. Meta-, if used as a prefix, is understood to imply alteration of the original rock-type to the name of which it is prefixed. Miaskite to be replaced by nepheline-syenite (Miask type). Mica-syenite is retained in the sense of a syenite with dominant mica. 142 EEPOET OF COMMITTEE ON Minette is retained in use for the igneous rocks at present so named. Monzonite should be restricted to rocks of the type occurring in the Monzoni district, Tyrol, typically augite-bearing and containing a note- worthy amount of basic plagioclase in addition to orthoclase. The term monzonite series may be used to comprehend related rocks whether more basic or more acid than monzonite itself. Nepheline-dolerite. Disuse recommended. See List B. Nephelinite, Leucitite, and Tephrite are to be retained in use in the sense at present adopted by British authors. They do not contain olivine as an essential constituent, but may contain it as an accessory. The names Nepheline-basalt, Leucite-basalt, and Basanite, are used so frequently that the Committee does not feel able to recommend their disuse, but it would prefer to see these terms replaced by olivine- nephelinite, olivine-leucitite, and olimne-teplirite. Obsidian. Glassy volcanic rocks of acid or intermediate composition, to be distinguished when evidence of composition is available, as rhyolite- obsidian, trachyte-obsidian, phonolite-obsidian, dacite-obsidian, andesite- obsidian. Oligoclasite. Disuse recommended. See List B. Ortho-. The use of this prefix as an abbreviation for orthoclase or to signify that a rock is rich in that mineral is not recommended. It is retained as a prefix to the name of a metamorphic rock to indicate igneous origin. Palaeopicrite. Disuse recommended. See List B. Pantellerite is allowable for rocks practically identical with those of the type locality, but preferably should be replaced by soda-rhyolite [or soda-trachyte] (Pantelleria type). Para- is retained as a prefix to the name of a metamorphic rock to indicate sedimentary origin. The significations given to this prefix by Loewinson-Lessing (1905), and by Lacroix (1920), are not adopted. Pegmatite. See under aplite. Peridotite. Holocrystalline igneous rocks of ultrabasic composition, rich in olivine, and free from felspar or containing it only as an accessory constituent. Certain olivine-rich rocks which have been described as hornblende-picrites should be included. Varieties should be described by prefixing the name of the mineral characterizing them. The names dunite and Iherzolite, being well established and clearly understood, may be retained. Perknite. See under pyroxenite. Picrite should be restricted to rocks of the type locality of Sbhle, BRITISH 1'ETEOGRAPHIC NOMENCLATURE. 143 Moravia, as described by Tschermak (1866), and to those closely similar rocks associated with teschenites and theralites in other regions. Pitchstone. Glassy rocks of similar range in composition to obsidian (q.v.), but characterized externally by pitchy lustre, splintery or hackly fracture, and a relatively high content of water. They are usually hypabyssal. Porphyrite. See under porphyry. Porphyritic texture. The definition given by Teall in 1888 (British Petrography, p. 51) is adopted, viz. : ' When . . . certain con- stituents occur as large or more or less perfect crystals in a matrix of finer grain the rock is said to be porphyritic. Porphyry and Porphyrite. Hypabyssal rocks of acid or inter- mediate composition with one or more porphyritic constituents in a crystalline (including cryptocrystalline) groundmass. Such rocks with dominant alkali-felspar are termed porphyry ^ as distinct from those with dominant soda-lime-felspar, which are termed porphyrite. These terms should be qualified by prefixing the name of the mineral or minerals which occur as porphyritic constituents. The name granite-porphyry is ambiguous, and should not be used. Pyroxenite. Those members of the perknite group with dominant pyroxene ; that is, in the original sense of Coquand, and the sense in which it is employed by Harker and Hatch. Perknite, introduced by Turner (1901), and adopted by Hatch (Igneous Rocks, 1914), may be usefully employed as a group name for : Holocrystalline igneous rocks ' composed of various combinations of hornblende, augite, and rhombic pyroxenes, together with accessory biotite, olivine and iron-ores. They . . . occur as deep-seated masses or as dykes.' Schist. See under gneiss. Shonkinite is retained in the sense of the original definition of Weed and Pirsson (1895), and the more detailed definition of Pirsson (1900). The rock of Square Butte, High wood Mts., Montana, described by Weed and Pirsson and analysed by the latter, is an olivine-bearing shonkinite with accessory nepheline, sodalite, etc., in small quantities. If, in certain varieties of shonkinite, leucite or nepheline become notable constituents, such rocks should be distinguished as leucite- or nepheline- shonkinites. Syenitite. Disuse recommended. See List B. Tephrite. See under nephelinite. Theralite is retained for nepheline-gabbros, the rock adopted as the type being the theralite of Duppau, Bohemia, and not the rock origin- ally described as theralite from Gordon's Butte, Crazy Mts., Montana. 144 REPORT OF COMMITTEE ON Tonalite should be replaced by quartz-diorite (Tonale type). Trachybasalt is adopted to replace the termtrachydolerite&s used by Washington in 1897, that is, for intermediate potash-rich rocks coniaining basic plagioclase together with orthoclase. The use of the term trachy- basalt in the sense of Boricky (1873) having been long discontinued, no confusion should arise from its re-introduction in a new and self- explanatory sense. Trachydolerite. Disuse recommended. See List B. Also see note under trachybasalt. Trachyte. Tyrrell's proposal to use trachyte, bostonite, and kerato- phyre, with textural significations for rocks which have essentially the same chemical and mineral compositions, regardless of whether they are of extrusive or intrusive origin, is not adopted. Wehrlite. Disuse recommended. See List B. Also see note under peridotite. LIST B. The following terms, which have been used in more than one sense, being either obsolete or unnecessary, it is recommended that their further use as petrological terms be avoided : Adamellite Domite Leucitophyre Auainesite Dunstone Leucotephrite Aphanite Euphotide Melaphyre Bauxitite Eurite Nepheline-dolerite Binary granite Felspar-rock Oligoclasite Cipolin Granitite Palaeopicrite Cornubianite Hyperite Syenitite Diabase Hypersthenite Trachydolerite Diallagite Leptynolite Wehrlite SYNONYMS. At its ninth meeting the Committee proceeded to consider a list of synonyms which had been circulated to members on April 27. As a result of the discussion the following list of terms for structures, textures, chemical characters, &c. (excluding rock-names), was drawn up. For each set of synonyms in this list the term printed in small capitals is the one the use of which the Committee recommends in preference to the alternative term, or terms, which are printed in ordinary type. ACCIDENTAL INCLUSION (Harker, 1900) : exogenous enclosure. ACID : persilicic. BRITISH PETROGRAPHIC NOMENCLATURE. 145 ALLOTRIOMORPHIC (Rosenbusch, 1897) : xenomorphic ; anhedral. Anhedral (Pirsson, 1895). See allotriomorphic. ARENACEOUS : psaminitic. ARGILLACEOUS : pelitic ; lutaceous. Autolith (Holland, 1900). See cognate inclusion. Automorphic (Rohrbach, 1886). See idioniorphic.. BASIC : subsilicic. COGNATE INCLUSION (Barker, 1900): autolith ; endogenous enclosure. CONTACT METAMORPHISM : exomorphism. CORONA : REACTION RIM : ; kelyphitic rim. Ellipsoidal structure. See pillow structure. Enclosure. See inclusion. Endogenous enclosure. See cognate inclusion. Euhedral. See idioniorphic. Exogenous enclosure. See accidental inclusion. Exomorphism (Fournet, 1867). See contact metamorphism. GLASSY : Hyalo- ; vitro-. HEMICRYSTALLINE : merocrystalline ; semicrystalline. Hyalo-. See glassy. Hypautom orphic. See hypidiomorphic. HYPIDIOMORPHIC : hypautomorphic ; subhedral. IDIOMORPHIC : automorphic ; eubedral. Included nodule. See inclusion. INCLUSION (in rock) : enclosure ; included nodule. INTERMEDIATE (silica content) : mediosilicic. Kelyphitic rim (Schrauf, 1882). See corona, reaction rim. 1 Lutaceous (Grabau, 1904). See argillaceous. Mediosilicic (Clarke, 1911). See intermediate. Merocrystalline. See hemicrystalline. MULLION STRUCTURE (Kinahan, 1891) : rodding structure. ORBICULAR STRUCTURE (Delesse, 1849) : spheroidal structure. Pelitic. See argillaceous. Persilicic (Clarke, 1911). See acid. PILLOW STRUCTURE : ellipsoidal structure. Psammitic. See arenaceous. PSEPHITIC : rudaceous. REACTION RIM ; CORONA : kelyphitic rim. 1 Roddiug structure. See mullion structure. 1 If the corona can be shown to be due to alteration or modification of the nucleus the term reaction rim is preferred 146 REPORT OF COMMITTEE ON Rudaceous (Grabau, 1904). See psephitic. Semicrystalline. See hemicrystalline. Spheroidal structure. See orbicular structure. Subhedral (Pirsson, 1895). See hypidiomorphic. Subsilicic (Clarke, 1911). See basic. Vitro-. See glassy. Xenomorphic (Rohrbach, 1886). See allotriomorphic. GENERAL RECOMMENDATIONS. The Committee makes the following recommendations for the forma- tion and mode of presentation of rock-names. With these are embodied the general resolutions passed at the second meeting of the Committee. It is desirable to avoid the use of a name or term in different senses, and to avoid the multiplication of terms to express the same rock, structure, or texture. While it is undesirable to assign new meanings to old rock-names it shall be permissible, if the old names are retained, to modify their defini- tions so as to conform to modern views of classification. When a new name is necessary for a rock, or group of rocks, it is preferable to make a name which is self-explanatory, and which conveys some idea of the relations of the newly-described rock, or group, to groups already defined, rather than to introduce a name, such as a place-name, which gives no information as to the affinities of the rock, or group, in question. When a mineral-name, or names, and a rock-name are compounded to form a name of l specific ' signification, these should be joined by a hyphen ; e. g. biotite-granite. But a mineral qualification of varietal character should be given in adjectival form ; that is with terminations such as : -ic, -iferous, -bearing ; e. g. hornblendic biotite-granite. When two mineral-names are of ' specific ' value the most important should be iplaced next to the rock-name ; e. g. biotite-quartz-diorite. When a particular type of rock, typically developed at one locality, is olearly assignable to one of the main rock-groups, and when, at the same time, the prefixing of mineral qualifications to a group-name cannot be made to describe adequately the rock in question, it is advisable to designate such rock by the group-name, followed in brackets by the name of the place coupled with the word type ; e. g. nepheline-syenite {Foya type) rather than ' foyaite '. This practice has been followed very successfully in the description of the Scottish basalts. Abbrevia- tions such as ' basalt (Markle type) ' to ' markle ', as used by certain BRITISH PETROGRAPHIC NOMENCLATURE. 147 authors, should be avoided . It is only permissible to use alternative expressions such as Markle basalt, Shap granite, when speaking of the rock of the type locality. Chemical qualifications, when used, should be in the form of substantives joined by a hyphen to the rock-name, e. g. soda-trachyte. ' Alkali- ' prefixed to a rock-name is understood to imply a relatively high content of either soda or potash or of both. When of these two alkalis one is definitely preponderant the word ' alkali- ' should be replaced by ' soda- ' or ' potash- ' as the case may be. In presenting their report the Committee wish it to be understood that they are not in favour of attempting to establish by national or even international councils a standard of orthodoxy in petrology. They recog- nize that petrological nomenclature is rapidly evolving, and their only object has been to assist if possible in the natural evolutionary process. How far they have succeeded will be shown by the extent to which their suggestions are adopted by petrologists who use the English language. (Signed) 1 W. W. WATTS, Chairman. GEORGE T. PRIOR. JOHN W. EVANS. E-. H. RASTALL. J. VINCENT ELSDEN. J. J. H. TEALL. J. S. FLETT. HERBERT H. THOMAS. F. H. HATCH. G. W. TYRRELL. W. CAMPBELL SMITH, December 15, 1920. Hon. Sec. 1 Dr. Arthur Holmes's signature has not been obtained, on account of his absence abroad. PUBLICATIONS OF THE MINERALOGICAL SOCIETY. (The Publishers are Messrs. Simpkin, Marshall, Hamilton, Kent & Co., Ltd., 31 $ 32 Paternoster Bow, London, E.G. 4.) All the Numbers (with the exception of Nos. 17, 19, and 22, which are out of print) can be supplied. The earlier Numbers vary in price from Is. to 5s. each (except No. 21, price 21s.) ; for Numbers published since 1889 (No. 39, Vol. VIII) the price is 55. net each. Volumes I, II, and III may be obtained, bound in cloth ; the prices of these are 135. 6d., 17s. (including map), and 12s. Qd. respectively. Later Volumes are only supplied in unbound Numbers, of which four or five form a Volume. 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Prior, M.A., D.Sc., P.K.S., Natural History Museum, South Kensington, London, S. W. 7. There is an entrance fee of one guinea and the annual subscription is one guinea ; the latter can be compounded for by a single payment of fifteen guineas. New members, on the payment of their first subscription, receive all the numbers of the current volume of the Magazine, and subsequent numbers as published. There are four meetings of the Society each year, on Tuesdays at 5.30 p.m. in January, March, June, and November. They are held (by kind permission) in the Apartments of the Geological Society, Burlington House, Piccadilly, London, W. 1. Titles of papers to be read at these meetings, with a view to subsequent publication in the Magazine, should be sent to the General Secretary at least two weeks before the meeting. Authors alone are respon- sible for the views set forth in their respective papers. They are allowed, free of charge, fifty separate copies of their papers published in the Magazine. MINERALOGICAL MAGAZINE CONTENTS OF NO. 92. (March, 1921.) PAGE L. J. SPENCER : Identity of Trechmann's ' fi-kin ' with stannous sulphide 113 H. H. THOMAS and A. F. HALLIMOND : A refract ometer for the determination of liquid mixtures 124 W. A. EICHARDSON : A method of constructing rock-analysis diagrams on a statistical basis 130 Report of the Committee on British Petrographic Nomenclature 137 MINERALOGICAL ABSTRACTS (No. 5, Pages 113-144.) Text-Books and Treatises (p. 113\ New Minerals (p. 119). Artificial Minerals, Crystallized Furnace Products, etc. (p. 125). Precious Stones (p. 127). Japanese Minerals (p. 132). Miscellaneous (p. 141). AMINOFF, G. . . . ARAI, K PAGE 124 139 PAGE HlNTZE. C. . . . 117 HlRABAYASHf, T. . 138 PAGE POGUE, J. E. . . . 130 POSNJAK, E. . . . 143 AWAZU, H. . . . BAYLEY, W, S. . . BEALE, W. P. . . BECKE, F. . . . BECKENKAMP, J. BENSAUDE, A. . . BOEGGILD, 0. B. BRAGG, W.H.&W.L BRYDONE, R. M. BUTLER, B. S. . . BUTTGENBACH, H. . CESARO, G. . . . CORTI, H CROOK, T. ... 138 114 113 118 114 144 123 113 143 119 114 127 120 115 HOLLOWAY, G. T. . 116 HOSHINA, M. . . 138 HOSTETTER, J. C. 125, 142, 143 HUNT, W. P. . . . 116 JIMBO, K. . . 132-134 KADOKURA, M. . 132, 135 KAWAMURA, M. . . 139 KRAUS, E. H. . . 116 KUNZ, G. F. . . 127, 128 LACROIX, A. . . . 123 LARSEN, E. S. . 120, 121 LAUBMANN, H. . . 124 LAUFER, B. . . . 128 PRATT, L. S. . . . 144 PURINGTON, C. W. . 131 READ, H. H. . . 110 RIMANN, E. . .121, 131 RUTLEY, F. . . . 116 SATO, D 137 ^CHALLER, W. T. 119, 128 SCRIVENOR, J. B. . 144 SETO, K 141 SHANNON, E. V. 122, 144 SMITH, C. M. . . 126 SOSMAN, R. B. 126, 142, 143 STEINMETZ, H. . . 124 DOELTER, C. . . . EAKLE, A. S. . . FT/INK, G. . . 123 FORD, W. E. . . . FUJIMURA, K. . . FUKUCHI, N. . 134 GEORGE, R. D. . . GILL, H. E. . . . GLENN, M. L. . . GROTH P. ... 117 122 , 124 115 141 , 135 115 120 121 117 MCDONNELL, C. C. . 120 MAKING, K. . . . 136 MAUZELIUS. R. . . 124 MERWIN, H. K. 125, 126, 143 MICHEL, H. . . . 131 MIDDLEMISS, C. S. . 130 MILKER. H. B. . . 119 NAKASHIMA, K. . 137 OTSUKI Y. . . . 139 SUTTON, J. R. . 129, 130 TAKIMOTO. T. . . 138 TSCHERMAK, G. . . 118 TSUBOI, S. . . . 110 WADA, T. ... 132 WADE, F. B. . . 128 WATANABE. M. . . 141 WATANABE, W. . . 139 WEINSCHENK, E. . 119 WELLS R C. . 120. IL'L* GUILD, F. N. . . HAMOR, W. A. . . BARKER, A. ... 122 126 118 PALACHE, C. . . . 122 PARSHAD, L. J. . . 130 PART, G. M. . . . 119 WHERRY, E. T. . . 120 YAGI, T. . . . 136, 137 YOSHIDA, H. . 135, 136 Oxford : Printed by FHKDKRK K HALT,, at the University Press MINERALOGICAL SOCIETY. (The Publishers are Messrs. Simpkin, Marshall, Hamilton, Kent & Co., Ltd., 31 ^32 Paternoster Row, London, E.G. 4.) All the Numbers (with the exception of Nos. 17, 19, and 22, which are out of print) can be supplied. The earlier Numbers vary in price from Is. to 5s. each (except No. 21, price 21s.) ; for Numbers published since 1889 (No. 39, Vol. VIII) the price is 5s. net each. Volumes I, II, and III may be obtained, bound in cloth ; the prices of these are 13s. 6d., 17s. (including map), and 12s. 6d. respectively. Later Volumes are only supplied in unbound Numbers, of which four or five form a Volume. A coloured geological and mineralogical Map of the Shetland Islands, by Prof. Heddle, issued with Vol. II (1879), may be had separately, mounted on cloth, with stiff covers, and 3 pages of description. Size 31 x 21 inches. Price 7s. 6d. ; or unmounted, with description, 5s. 6d. A coloured geological and mineralogical Map of Sutherland, by Prof. Heddle, issued as No. 21 (1881), mounted on cloth, in cloth case, with 8 pages of description. Scale 2 miles : 1 inch. Price 21s. Index of Authors and Subjects, Vols. I to X. Price 5s. Mineralogical Abstracts, Nos. 1-4 (1920). Price 2s. 6d. net each. 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They are held (by kind permission) in the Apartments of the Geological Society, Burlington House, Piccadilly, London, W. 1. Titles of papers to be read at these meetings, with a view to subsequent publication in the Magazine, should be sent to the General Secretary at least two weeks before the meeting. Authors alone are respon- sible for the views set forth in their respective papers. They are allowed, free of charge, fifty separate copies of their papers published in the Magazine. MI]SrERALO(H A T *'" TINE 14 DAY USE RETURN TO DESK FROM WHICH BORROWED EARTH SCIENCES LIBRARY stannous This book is due on the last date stamped below, or - 1 Q on the date to which renewed. TT Renewed books are subject to immediate recall. I* >r for the 13C . 124 (-analysis . . 130 enclature 137 tificial Minerals, les (p. 127). PAGE J. E. . . . 130 c, E. . . . 143 L. S. . . . 144 TON, C. W. . 131 L H. . . 116 , E. . . 121, 131 F. . . . 116 137 :R, W.T. 119, 128 w R< Te: AM AB A^ r> , BE. BE< BE< BEI BOJ BR. BR- Bu: OR, J. B. . 144 141 v, E. V. 122, 144 3. M. . . 126 R. B. 126, 142, 143 TZ, H. . . 124 J. R. . 129, 130 ro, T. . . 138 [AK, G. . . 118 S. . . . 140 1\ ... 132 ?. B. . . 128 BE. M. . . 141 BE, W. . . 139 IENK, E. . 119 R. C. . 120. li>i> ', E. T. . . 120 ... 136, 137 , H. . 135, 136 BIT CES Co* CRC Doi T^\l FLI FOE "P TTT FUB T-no-t /n,in'rc General Library GEO L ?/ 77 63si m OH76 5 Univem^rfglilomta GROTH, P. . . . 117 OTSUJ :i, Y. ... 139 WELLS, 3HE, C. . . . 122 WHERin AD, L. J. . . 130 YAGI, T. G. M. . . . 119 YOSHIDA GUILD, P. N. . . 122 PALA( HAMOR, W. A. . . 126 PARSI BARKER, A. . . . 118 PART, Oxford : Printed by FREDERICK HALL, at the University Pross Gay lord Bros, Makers Syracuse, N. Y. PiL JAN. 21 ,1908 EARTHS I3RARY