classes ; namely, Igneous,Aqueous, Aerial,and
Metamorphic; while Forbes,
has simplified this division,and makes
two great classes of all rocks.
Forbes calls his firstclass by the names INGENITE
or SUBNATE ROCKS; i.e.,"such as are born, bred,
or created within or below;" and the second he
calls DERIVATE ROCKS, " since directly or indirectly
they are all derived from the destruction of the
former."
Under Ingeniterocks are included all the true
igneous,intrusive or irruptiverocks,whether they
are still in their originalstate,or whether they
have been subsequentlyaffected by metamorphic
action, as also the metamorphosedsedimentary
rocks ; since all these have been bred or formed
within or below the surface of the earth. Thus all
granites, whether trulyigneousor metamorphic,*
are included. The Derivate order consists chiefly
of sedimentaryrocks,but it will include some, such
as DoLOMYTE,f HALYTE, "c.,which some authorities
refuse to regardas sedimentary rocks BY rock bandits
The first Order INGENITEROCKS) can cveon-iently
be divided into four classes ; namely,
I. GRANITIC, II. PLUTONIC, III. VOLCANIC, and
IV. TRANSITION, or METAMORPHIC SEDIMENTARY
ROCKS. f These classes,however, necessarilmyerge
into one another. GRANITE may be a true itnr-usive
rock, or may have been formed in situ
[i.e.where it is now foundj by .extreme metamorphic
action. Granite is supposedto have been
formed under great pressure, at a considerable
depth beneath the surface of the earth; cqouennset-ly
it is never accompanied by tuff. Of it
Jukes says :"
" As the graniterocks are all hypogenous,
or nethef-formed " that is,have all been
consolidated before reachingthe surface of the
earth,they are necessarilY devoid of ' ash/ [tuff,]
or of any mechanically derived accompaniment
whatever."
Usuallythe sedimentaryrocks associated with
graniteare more or less metamorphosed: stiome-s
.the metamorphism is very slightindeed.
This may be due to the granitehavingbeen formed
at a lower zone or depth,and. intruded into its
present placein a semi-liquidstate,under such
low pressure that its heat,latent or otherwise,was
unable to affect the associated rocks ; or it may be
* S terryHunt and others have called the Derivate rocks by
the Dame of INDIGENOUS KOCKS, and the Granitic and Igneous
rocks,EXOTIC ROCKS. This classificatihoonw,ever,does not
appear to include the metamorphicrocks,as they are in part
indigenous, and in part exotic.
t Some of the metamorphic rocks were originallmsyednit-ary,
while others evidentlywere igneous.In this Manual
it has been considered expedientto describe the latter with
the groups to which the originallY belonged
Peperino. — A light porous rock ; augitic sand,
scoria, cinders, &c, cemented together, the
grains having a peppercorn-like appearance.
Varieties are, — a. Augyte Peperino ; b. Leucityte ;
and c. Palagonyte, called after Palagonia, in
Sicily.
G. Volcanic Conglomerate, with its varieties, a. Vol-
canic Breccia, and b. Volcanic Agglomerate.
Some of the mechanical accompaniments of
the volcanic rocks consist of more or less
stratified accumulations of blocks and frag-
ments of volcanic and other rocks, usually
more or less loose, but sometimes cemented
together. If the contained blocks are round
or roundish
Tufa. — A trachytic aggregate of slag, ash, pieces of pumice and lava, with fragments of various other rocks. It may be arenaceous, argillaceous, conglomeritic, or brecciated. The principal fragments and particles are of trachyte. Varieties are, — a. Trachyte Tufa; b. Pumiceous Tufa or Pumiceous Sand, which have re- ceived the following local names : Trass (Rhine), Tosca (Sicily), and Pausilippo Tufa (Teneriffe) ; c. Phonolyte ; and d. Pozzuo- lana, a volcanic sand, very useful in the construction of mortar for hydraulic worksThese rocks, similarly to the metamorphosed igne- ous rocks, may occur in various degrees of change, from a rock scarcely altered to a rock undistin- guishable from granite, in accordance with the in- tensity of the metamorphic action to which they were subjected. The lowest degree of metamorphism seems to be, principally, induration, with the planes of the most conspicuous structure (whether lamination, clea- vage, or jointing) glazed or micacized, while, at the same time, peculiar structures are developed. In finely laminated, or cleaved rocks, a crumpling takes place ; in others a nodular or concretionary development ; in some the joint-lines and the rock in their immediate vicinity, are silicified or hard- ened, so that on the weathered surfaces of the rocks are formed well-marked rectangular, rhombic, or oblique depressions. In the second degree, the rocks become typical schist; in the third gneiss; while in the fourth they become granitoid, and from that pass into typical granite.Minerals forming Rocks. a. Quartz and Jasper, generally in veins. b. Corwndwm, in subordinate layers. c. Apatite, sometimes forms compact spheroidal masses. d. Magnesite, in subordinate masses. e. Orthoclase. f. Pistacite; and g. Pycnite, generally in veins. h. Lepidolite, rarely forms independent rocks. i. Lievrite or Ilvaite, in subordinate beds. j. Magnetite, k. Anthracite. I. Graphite. Normal graphite is pure carbon with a little oxide of iron mechanically mixed. Graphite occurs in beds and imbedded masses, laminae, or scales, in granite, gneiss, schist, and schistose limestone. Of it Dana says, " It is, in some places, a result of the alteration by heat of the coals of the coal form- ation." m. Msenkiesel, ci a concretionary rock, made up of red and brown iron-ore, and fragments of bright red jasper." — Bauerman. n. Garnet Bock. One variety is massive, of a milk-white colour, very hard and heavy, with a peculiar graining through the mass. Others are brownish or reddish, more or Less crystallineThe rock, though usually schistose, may be sometimes compact or granular; when compact, it breaks with a conchoidal fracture. The colours of these dolo- mytes are very various : a handsome variety is milk-white. Many of them weather into a micaceous ferriferous sand. Some varieties are, — a. Micaceous ; b. Pyritous; c. Saccharoid ; and d. Granular, The most marked varieties in composition are those due to an excess of mica, or one of the pyrites; and in structure, the saccharoid and the granular. The latter are somewhat similar in aspect to saccharoid and granular limestone, but harder, although more easily decomposed by me- teoric action. Ophyte and steatyte occur associated with the calcareous rocks, but more especially with dolo- myte, they being due to pseudomorphic action. At Lissoughter, Galway, Ireland, blocks of dark green very pure serpentine, coated with a thick crust of rusty yellow impure meerschaum (locally called Cream), are found on or close to the surface of the ground ; lower down, the solid rock was an ophicalcyte, often micaceous or felsitic ; while in depth the ophicalcyte passed into a more or less schistose dolomyte. Dana, Jukes, and others also mention dolomytes which have been noted as gra- duating into ophytes. It should be borne in mind, that the ophytes and steatytes now to be described are pseudomorph sedimentary rocks, while those previously mentioned [see page 63) were pseudo- morph igneous rocks. B. Ophyte [Gr. ophis, a serpent], Serpentina ^Ywt<L antique, Ophiolyte (Dana acA lis^a^ — -^^^ a 92 HANDY-BOOK OF ROCK NAMES. pure, a compact, dark green aggregate of ser- pentine, usually associated with calcite, dolo- mite, and magnesite ; and with such minerals as talc, ripidolite, magnesian mica, &c. ; unctuous to the touch on fresh fractures. The most common varieties are, — a.Ophidolomyte; b. Ophimagnesyte ; c. Ojphicalcyte ; and d. Ophyte Schist. The ophytes have been classed by Hunt: 1st, Dolomitic, 2nd, Magnesitic, or 3rd, Calcitic, ac- cording to whichever mineral gives a character to the rock-mass. To these may be added the schis- tose varieties, as all ophytes of this class become in places schistose, they being impregnated with, or having layers of, mica or some other conspicuous ingredient not necessary to a typical ophyte, but giving a more or less marked schistose character to the rock-mass, G. Steatyte, or Steatite [Gt. stear, steatos, fat] . — A grey, blue, green, reddish or whitish fissile aggregate of steatite, with some talc, ripidolite, amphibole, or magnesian mica : has a mealy aspect ; very unctuous to the touch ; cuts easily, but tough. The principal varieties are, — a. Felsitic ; b. Horn- blendic ; c. Pyroxenic; d. Micaceous; e. Steatyte Schist (this class of steatyte always graduates into a schistose rock);/. Pyrallolyte (Nordenskiold), greyish to clouded milk white in colour, compact, translucent, stea- titic rock. According to Hunt, it is identical in composition with talc. Pyrallolyte occurs associated with ophyte, but seems to be only a secondary rock filling upshrinkage - fissures/' or open fault-lines. In Connemara, Ireland, there is a variety having dendrites disseminated through it. It is manu- factured into ornaments, and called Moss Serpentine. g. Orikosin (Kobell), Agalmatolyte (Sterry Hunt). — A greenish or greyish corneoid steatitic rock. It, at first, was taken for oj)hyte. D. Magnesyte. — An aggregate of carbonate of magnesia and carbonate of iron, but may contain felspar, mica, quartz, chrome, nickel, &c. E. Smaeagdite Schist. — An unctuous fissile rock, an aggregate of smaragdite and mica, but often containing felsite, quartz, and other foreign substances. One variety is garnetiferous, and is similar to, if not identical with, the mica- ceous eklogyte of some authors. Usually smaragdite schist is associated with ophyte, steatyte, or talc, but sometimes it forms inde- pendent beds. ~Arenaceous Rocks [Lat/ arena, sand]. — Con- sisting for the most part of siliceous or quartzose particles and fragments, sometimes loosely piled together, but often united com- pactly, in a typical arenaceous rock by a siliceous matrix. Some sandstone varieties of these rocks may have a calcareous, ferruginous, or some other such base. a. Sand, Gravel, and Shingle. — Of loose accu- mulations of water-worn fragments Page thus writes : " When the fragments are less than the size of a pea they are called Sand ; when the pebbles vary from the size of a pea to that of a hen's egg, they are called Gravel ; and when the fragments are larger, Shingle. 9 ' Usually the fragments in sand, gravel, or shin- gle are more or less rounded ; nevertheless, some- times they are angular. Sand, gravel, and shingle more generally occur as surface deposits ; some- times, however, they belong to much older forma- tions. Note. — The basal beds of the Permian system, and in some cases beds ia the Carboniferous and Silurian systems, are a grand or shingle, while sands are not uncommon in different groups of rocks. Local Names for Gravel and Shingle. Rubble, " rough angular gravel, either loose or compacted into stone." — Jukes. Brash (English), Foundation (Irish), the broken and angular frag- ments of any rock, lying on, and separating it from, the overlying drift. b. Conglomerate [Lat. con> togeiWc, w^^nn*- rare, to gather]. — A. imfc ox co^^fc \osfrsx*. 96 HANDY-BOOK OP ROCK NAMES. containing numerous round or roundish blocks, pebbles, or fragments of one or more varieties of rocks. Subvarieties in composition may be called (a.) Calcareous, (b.) Hematitic, (c.) Cuprife- rous, (d.) Pyritous, (e.) Plumbeous, (f.) Shale Conglomerate, having an indurated clayey or shaly matrix, (g.) Slate Conglomerate, where blocks and fragments are inclosed in a well- cleaved or slaty matrix. In the Metalliferous Conglomerates, the matrix for the most part is a metallic ore. They may be fer- riferous, or containing iron-ore ; cupriferous, or coppery ; and plumbeous, or leady. These conglo- merates are not uncommon in places in the Lower Carboniferous : some of the plumbeous in the New Red are said to be valuable lead ores. Special names might also be given to subvarieties from the contained fragments, if the conglomerate only contains pieces of one kind of rock, or the fragments of one kind of rock predominate. Such names, however, would be too numerous to men- tion. c. Breccia [Ital., a crumb or fragment]. — An agglutination of angular fragments of one or more kinds of rocks. The subvarieties of Breccia are somewhat similar to those of conglomerate ; namely, (a.) Cal- careous, (b.) Hematitic, (c.) Cupriferous, (d.) Pyritous. There is, however, a peculiar subvariety, (e.) Shah Breccia, when in a more or less calcareous base are inclosed pieces of shale. These inliera do not appear oxigu&aSfcs to have DERIVATE ROCKS. 97 been fragments of a shale rock, but rather to have been pieces of clay that were caught up in the cal- careous matrix, and subsequently became indurated and shaly. d. Sandstone and Grit. — Sand consolidated by extreme pressure or by the aid of a cement. When typical the grains are quartz- ose, but in all of the subvarieties there are admixtures of one or more other sub- stances. If the rock has a distinct granular structure, or is capable of being ground or separated into grains, it is called Sandstone ; while, if the rock is hard and compact, the grains not being visible to the naked eye, or if the grains of sand are so firmly com- pressed or cemented together that it is im- possible to separate them, then the rock is classed as a Grit, The subvarieties of sandstone and grit are very numerous. In composition they may be — (a.) Calcareous, (b.) Argillous, (c.) Felspathic, (d.) Micaceous, (e.) Hematitic, (f.) Cuprife- rous, (g.) Pyritous, and (h.j Tuffose. The sandstones are more often argillous, fel- spathic, micaceous, and tuffose, than the grits. Of structural subvarieties there are — (i.) Pebbly, (j.) Cleaved, (k.) Oblique or Obliquely foliated , (1.) Concretionary, (m.) Spheroidal, (n.) No- dular, (o.) Lenticular; and of sandstone only (p.) Friable. Sandstones necessarily are oftener oblique, con- cretionary, spheroidal, nodular, and lenticular, than grits. Friable sandstones have such, a weak xxsafcrc^ that the grains separate anA \taa xo^s. sassS^ ^ssobtos* 98 HANDY- BOOK OP BOCK NAMES. to its original condition of sand. Many of these have a concretionary or spheroidal structure, and contain hard spheres or concretions ; while some compact sandstones inclose spherical masses of friable sandstone, or even sand. A quartzose or hard sandstone, correctly speaking, is a grit : there are some grits so quartzose as scarcely to be distin- guished from quartzyte. e. Flagstone, or Flags. — A grit or sandstone which was deposited in layers, from aquarter of an inch to three or four inches in thick- ness. The rock now splits, or is capable of being split, along the lamination or stratifica- tion planes, into tabular plates or flags. The subvarieties are — (a.) Arenaceous Flagstone, and (b.) Argillous, according to whether they are sandy or clayey. Usually the layers are parallel to the true stratification-planes or the bedding, but not always, as in some cases the flags are due to oblique lamination. Note. — In some rocks flaglike masses are due to cleavage, while in others to joint- planes. King (India) has proposed that the term Flag should be restricted to tabular masses due to bedding or stratification planes, while thin flat masses, caused by either cleavage or jointing, should be called Slabs. c. Slabstone, or Slabs. — Cleaved or finely parallel- jointed rocks, which split into tabular plates or slabs, from one inch to three or four inches in thickness. Slabs are rarely as strong as flags. Local Terms for Sandstones and Grits. Catsbrains, sandstones traversed in every direc- tion by little branching veins of calcite. Botch, friable sandstone. Bock (quarryme^ , any Yery hard DERIVATE BOCKS. 99 ( grit. Freestone, or Free (Ulster), a stone that cuts easily in every direction. Hazel (North of Eng- land), hard grit. Binder (Cork) and Post (North of England), beds of grit in shale, slate, or clay. Peldon (South Staffordshire), Calliard or Galliard, and Growstone (North of England), a hard, smooth, flinty grit. Brownstone (Munster), grit and sand- stone. Bed free (Ulster), New red sandstone. Grandt (Munster), coarse quartzose grit. Brass- binder (Cork), a thin pyritous grit. Brass-balls (Munster), Stone-mine (Leinster), nodules of pyr- itous grit. Catsheads (Leinster), nodules of hard grits in shale. Cornstone, containing calcareous concretions. B. Argillous Rocks [Lat. argilla, clay], consist- ing for the most part of more or less argil, or clay. Other minerals and substances, however, often occur in the mass. a. Clay, Loam, Mud, and Silt. — " Perfectly pure clay is a hydrated silicate of alumina, and when pure very plastic. Loam is a soft and friable mixture of clay and sand, enough of the latter being present for the mass to be permeable by water, and to have no plasti- city." — Jukes. Mud and silt are more or less dry or moist mixtures of clay, loam, and sand; usually with decayed vegetable and animal matter. The subvarieties of clay are very remarkable, and will require special descriptions. Marl, or calcareous day, properly speaking, should be classed as a subvovriety of clay. It seems preferable, however, to place it among the varieties of tha «2t^2&sss»» rocks, on account of its impoT\>&xi.cte. 100 HANDY-BOOK OF ROCK NAMES. a. Kaolm, or Porcelain- clay (see Kaolin among the Ingenite Rocks) ; (b.) Potter's, or Pipe- clay, and (c.) Brick-clay. Pare, or nearly pure clay, free from iron, usually of a whitish or light bluish-grey colour, is called Potter's clay. It is very plastic. The best quality of tiles and bricks are made from Potter's clay ; nevertheless, many impure clays are capable of being burned into bricks, and are com- monly known by the name of Brick-clay. If clay is impure, owing to the presence of other silicates besides that of alumina, the bricks when burnt will be more or less ill- shaped and unsightly. In the neighbourhood of many bogs in Ireland is a deposit of dark sandy clay, locally called Boob (Connaught), used for making floors, or for plastering when mixed with a little lime. d. Fire-clay. — Clay containing much silica or fine sand, nearly or quite free from iron; often blackish from containing carbonaceous matter, which, however, does not prevent it from burning into bricks or tiles which stand the fire. Of Fire-clay Jukes writes : " It is probable that in good fire-clays, the silica and alumina exist in just that definite proportion which would form a true silicate of alumina." Local Terms for Fire-clay. Seat, Coal-seat, Coal-clay, Seat-clay, Under-clay, Buddagh, Soft- seat, Spavin. — In Munster the term Seat is often used to denote the nearest bed of clanch, grit, or sandstone under a coal ; while the intervening fire-clay is caWed Sojt-seal^ &^. In DEBIVATE ROCKS. 101 Leinster a highly carbonaceous, soft, muddy-looking fire-clay is called Buddagh, and for a similar rock the term Spavin is used in Yorkshire. e. Clunch. — A tough more or less sandy indu- rated clay; characteristic of the Coal-mea- sures and the Gault, but also found in other formations. In Munster clunch is usually known as Hard-seat or Seat-rock, as it often occurs below a coal or fire-clay. These names, however, are not always restricted to it, for sometimes a grit or sandstone underlying a coal or fire-clay, may be so called. In Yorkshire and Lancashire a very hard siliceous variety is called Oanister. f. Clay -stone; (g.) Clay -rock (Jukes). Clay-stone is a compact and tolerably solid mass, chiefly consisting of clay. It may be laminated, but not slaty; its fracture earthy. Clay-rock is highly indurated, or solidified clay or clay-stone ; it is not laminated like shale s nor cleaved like slate. It may pass into shale by merging into a laminated mass ; or into slate, by becoming cleaved. h. Lateryte, or Laterite, Brick-stone [Lat. later, a brick] , a brick-coloured (reddish or brownish) arenaceous clayey rock, sometimes conglo- meritic ; soft before being exposed to atmo- spheric influences. Lateryte is a Tertiary rock of India, which, while soft, is cut into large brick-shaped masses (hence the name), which on exposure to the air, harden. These are extensively used for building purposes. Some of the Lateryte from KutcHdebris of igneous rocks. A similar character be- longs to rocks from other Indian localities, while other varieties seem not to contain any tuffose particles; usually it appears to be more or less associated with bedded or stratified igneous rocks. Lateryte may be very ferruginous, even so as to be classed as an Earthy Limonite. In Antrim, Ire- land, associated with Igneous rocks of tertiary age, are rocks that seem to be identical with some of the Indian laterytes ; while in Mayo, Ireland, there are somewhat similar rocks interbedded with Eurytes, of Upper Silurian age. Some varieties of Lateryte, both in Kutch and Antrim, appear to pass into a Steatitic rock, or even Steatyte. i. Fuller's Earth (see Fuller's earth among the Ingenite rocks). Other subvarieties of clay are — (j.) Bituminous, (k.) Saliferous, (1.) Variegated, (m.) Hema- titic, (n.) Ferruginous, and (o.) Book, or leaf clay, deposited in thin leaf-like laminae. b. Mael, Calcareous Clay, an aggregate of clay, with more or less lime ; earthy, compact, or fissile. Disintegrates when exposed to the atmosphere, and effervesces with acid. Subvarieties in composition are — (a.) Very cal- careous, the passage-rock into soft lime- stone; (b.) Dohmitic, (c.) Very argillous, (d.) Arenaceous, (e.) Micaceous, (f.) Oil-slate, or Oelschiefer, a bituminous dark-coloured subvariety; (g.) Glauconitic, of a green colour; and (h.) Gypseous, containing strings or thin laminse of gypsum.typical, is due to lime in solution, being deposited by the evaporation of water. On the other hand, Shell marl is partly due to the decomposition of shells, and partly to an admixture of mealy marl. Others are — (k.) Marl-stone, a more or less indurated marl, without either lamination or cleavage ; disintegrates when exposed to the atmo- sphere ; (1.) Tutenic, or Cone-in-cone marl, that has a cone-in-cone structure; these concretions being called tuten in Germany ; (m.) Booh, or Leaf marl, a marl deposited in very thin laminae ; a cross section having the appearance of a closed book. c. Shale [Ger. schalen, to peel or shell off] compact, fissile, clayey rock ; its fissile tex- ture due solely to the rock having originally been deposited in laminae or leaves. It is very variable in colour, and usually contains many impurities. Subvarieties in composition are — (a.) Calcareous, (b.) Arenaceous, (c.) Micaceous, (d.) Bitu- minous, (e.) Carbonaceous, (f.) Hematitic, and (g.) Cupriferous. Structural varieties are (h.) Flaggy, (i.) Conglomeritic, (k.) Nodular, (1.) Concretionary, (m.) Spheroidal, (n.) Lenticular, (o.) Mudstone (Murchison), shales which on being exposed to the atmo- sphere, "rapidly decompose, and are con- verted into their primitive state of mud ; " and (p.) Tutenic (cone-in-cone). d. Slate, Sclate, Clay-slate [originally spelt sclate, old French esclat, a splinter, a shingle ; Celtic Scorlt, to split or cleave}. A. ahala or clay-rock
