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lains, they are denominated upfillings. And rocks that compose them, follow one another in when a portion occurs only on one side of a rising from the lower levels toward the higher ; mountain, it is said to be shield-formed, or to or, in other words, are placed above one anohave the shape of a shield.
ther, not in an irregular or promiscuous manner; 3. Of the position and direction of strata in re- they follow a certain order of succession, and gurd to the fundamental rock.- When strata exhibit certain determinate relations. We do have the same direction as the fundamental rock, not, for instance, find a stratum of granite alterthey are said to be conformable with it; if the nating with a stratum of sandstone, nor a formadirection is different, they are said to be un- tion of gneiss covering a bed of pit-coal. In conformable. If they differ only in direction, examining the crust of the earth to discover this we say that they are simply unconformable; order of supraposition we observe a great class but if they differ not only in direction, but lie of rocks pushing in alpine chains, their summits over the ends of the strata of the fundamental above all the flatter strata, and affording on their rock, they are said to be unconformable and sides, and at their base below, a resting place, or. overlying. Overlying strata occur more fre- support for them. These rocks are found under quently than simply uncomformable, and have every other stratified mass, and never covering, far greater extent.
or resting upon, any. 4. Of the direction of the strata themselves, In like manner the rest of the strata have cerwithout reference to the fundamental rock.- tain relations to each other, from the granite to Strata are either straight, that is, disposed in one the most superficial mould. direction on the fundamental rock, or they turn III. We proceed now to the third division of around it, and enclose it; in this case they are said the subject of geology, which was to give a short to be mantle-formed, or mantle-shaped. If the view of the various classes of rocks and mineral strata are not only wrapped around the funda- masses, that compose the earth's crust, arranged mental rock, but also cover its extremities, they according to their relative situation. We shall are said to be saddle-shaped.
best execute this part of our duty, by presenting When the upper part of the saddle-shape is to our readers Dr. Thomson's compressed, but carried away, the mantle-shape is formed. comprehensive account of the Wernerian ar
Strata are sometimes concave, and they are rangement, drawn up with his usual acuteness, then said to be basin-shaped ; but, if the conca- and displaying his usual extent of information vity be oblong, they are named trough-shaped. and research. Some of the observations may be In the concave, that is, the basin and trough- found in the article MINERALOGY, and under shaped, and convex, that is, the saddle and man- the titles of the different minerals to which they tle-shaped strata, the outgoings form circles; in refer; but we could not on that account omit the concave the outer and greatest circle is the the repetition of them, without destroying the oldest; in the convex, on the contrary, the outer continuity and systematic connexion of this and largest circle is the newest.
article. 5. Of the relation of the outgoings of the strata Werner has chosen the relative situation of to the exterior of the mountain.We have to con- rocks as the basis of his classification. He disider, first, the relation of the outgoings of strata vides them into five classes. The first class conto mountain-masses of considerable extent; and, sists of those rocks, which, if we were to suppose secondly, to mountain caps.
each layer to be extended over the whole earth, In mountain-masses, the strata either cover would in that case lie lowest, or nearest the each other completely, or the outgoings are open centre of all the rocks which we know, and be and exposed. When the outgoings are exposed, covered by all the other rocks. The second class the newer strata have a rising or sinking level. consists of those rocks which in that case would
There are three different kinds of mountain- be immediately above the first class, and cover caps. In the first, the cap rests on a fundamen- them. The third class would cover the second tal rock; the seams of the strata are parallel with in the same manner; the fourth the third; and the the plane on which the strata rest, and these are fifth would be uppermost of all, and constitute the unconformable and overlying ; the second kind immediate surface of the earth. The first class of cap is formed by a rock rising through the sur- of rocks are covered by all the rest, but rever rounding strata ; and the third kind of cap is themselves lie over any other. The others lie in formed by portions of harder beds remaining order over each other. These grand classes of after the superincumbent and softer strata have rocks he has denominated formations, and disbeen carried away.
tinguished them by the following specific names : In the first, the rock is unconformable and 1. Primitive formations; 2. Transition formaoverlying. The flætz-trap and porphyry forma- tions; 3. Flætz formations ; 4. Alluvial formations afford numerous examples of this kind of tions; 5. Volcanic. mountain-cap.
The primitive formations are of course the In the second, the newer strata are mantle- lowest of all, and the alluvial constitute the very shaped. Granite 'often occurs in caps of this surface of the earth; for the volcanic, as is obkind.
vious, are confined to particular points. Not " In the third, all the strata are conformable, so that the primitive are always at a great depth that the subjacent and superincumbent strata have under the surface, very often they are at the surthe same direction with the bed which forms the face, or even constitute mountains. In such cap. Primitive greenstone, in clay-slate, some- cases, the other classes of formations are wanting times forms caps of this kind.
altogether. In like manner the transition, and · These strata and formations, and the kinds of other formations, may pach in its turn occupy
the surface, or constitute the mass of a mountain. 13. Newer porphyry.
Let us consider each of them in the order of Each of these grand classes of formations con- the formations. sists of a greater or smaller number of rocks, 1. Granite is the lowest of all the formations, which occupy a determinate position with respect and the basis upon which the others rest. It is to each other, and which, like the great forma- composed of felspar, quartz, and mica; each in tions themselves, may often be wanting in parti- a crystallised state, and cohering together withcular places. Let us take a view of the rocks out any cement. The felspar is usually the most which compose all these different formations. abundant ingredient, and the mica the smallest
in quantity. The color of the quartz and mica Class I.-PRIMITIVE FORMATIONS. is usually gray; but the felspar has a consideraThe rocks which constitute the primitive for- of white, gray, red, and green. The size of the
ble variety of colors, occurring in different shades mations are very numerous. They have been
constituents of granite varies considerably. Somedivided therefore into seven sets; which consti- times the grains are very large, and sometimes tute as many primitive formations, and are dis- they are so small that the granite has the appeartinguished each by the name of that particular
ance of a sandstone. Sometimes it is porphyrock which constitutes the greatest proportion of ritic, large crystals of felspar occurring in a basis the formation. These seven sets of primitive of fine-grained granite. Sometimes this rock is formations are the following :-1. Granite; 2. distinctly stratified, but in other cases no stratifiGneiss; 3. Mica-slate; 4. Clay-slate ; 5. Newest cation can be perceived. The unstratified or primitive porphyry; 6. Sienite ; 7. Newer ser- massive granite is frequently composed of large pentine. The granite is the undermost, and the sienite globular masses, each of which is composed of
concentric lamellar distinct concretions. The the uppermost of the primitive formations, Gra- intervals between these halls consist of a softer nite is scarcely mixed with any other rock; but granite, subject to crumble down when exposed in gneiss, mica-slate, and clay-slate, there occur
to the action of the weather. beds of old porphyry, primitive trap, primitive Besides the three constituents of which granite limestone, old serpentine, quartz rock. For that
essentially consists, other crystallised minerals reason, these rocks are said to constitute forma- occasionally occur in it, though only in small tions subordinate to gneiss, mica-slate, and clay- quantities. These crystals are chiefly of schorl; slate. Gypsum occurs in beds in mica-slate, sometimes garnet and tin-stone. and old Hint-slate occurs in the same way in
Granite very seldom contains among its strata clay-slate. Thus, besides the seven principal beds of any foreign rock. Beds of felspar alone primitive formations, there occur seven subordi- have occasionally been observed in it. It is not nate formations, interspersed through the second, so rich in ores as some of the other formations. third, and fourth formations; and topaz rock, Tin and iron are the metals which are most which lies over gneiss and under clay-slate, must abundant in it. Hitherto molybdena has been be added to the list; so that the primitive for- found chiefly in granite. It contains also silver, mations altogether amount to fifteen.
copper, lead, bismuth, arsenic, cobalt, tungsten, If we suppose the nucleus of the earth to have and titanium. been first formed, and the formations to have
Besides the great granite formation, which has been afterwards deposited in succession upon been just described, Werner has discovered a this nucleus, it will follow that the lowest forma- second; which is supposed to occur nearly in tion is the oldest, and that the formations are the same geognostic situation as porphyry and newer and newer according as they approach the sienite. The granite veins which iraverse gneiss, surface. This supposition accounts for some of mica-slate, and clay-slate, belong to this formathe names given to the primitive formations. tion. There are several particularities by which That porphyry, for example, is considered as the this newer granite may be distinguished from the oldest which lies lowest down in the series of other. It usually occurs in a lower level; it formations, and those formations of porphyry has commonly a deep red color; contains garwhich lie nearer the surface are considered as nets; and is not porphyritic. newer. Granite, of course, according to this
When granite is not covered by any other forway of speaking, is the oldest
formation of all
, mation, forms high insulated cliffs and steep while the alluvial are the newest of all. The
rugged rocks. following table exhibits a synoptical view of the
2. Gneiss is the formation which lies immeprimitive formations :
diately over granite, and into which indeed it
gradually passes. Gneiss consists of the same Principal.
constituents as granite ; namely, felspar, quartz, 1. Granite.
and mica; but it differs in its structure, being 6. Older porphyry. disposed into slates from the prevalence of the
7. Primitive-trap. mica. The texture of the individual slates is 2. Greiss.
8. Primitive limestone. . granular. Hence the structure of gneiss is 3. Mica-slate. 4. Topaz-rock.
9. Older serpentine. granular slaty. Gneiss is always distinctly strati
10. Quartz. 5. Clay-slate.
fied. It sometimes contains crystals of schorl; 11. Gypsum.
but they are smaller and much more uncommon (12. Older flint-slate than in granite. Tourmaline is more common,
and so likewise is garnet. It contains in it nate formations. It contains also a considerable many foreign beds, which is not the case with number of metallic ores in beds; as irou pygranite. Beds of three of the first sis subordi- rites, copper pyrites, arsenic pyrites, cobalt, ga nate forniations are found in it. It is, perhaps, lena, &c. It contains also a variety of mineral richer in metallic ore than any other formation. veins. Almost every metal occurs in it, either in beds Having now described the first four primitive or veins.
formations, let us proceed to the subordinate When gneiss is not covered by any other forma- formations ; taking topaz rock along with them, tion, it forms round-backed mountains, and like- on account of its rarity. These are the older wise crags : but less steep and insulated than porphyry, primitive trap, primitive limestone, those composed of granite.
older serpentine, quartz, topaz rock, gypsum, and 3. Mica-slate.—The formation which lies im- primitive flint-slate. mediately over gneiss, and into which it insensi- 5. Older porphyry.-By porphyry, as defined bly passes, is mica-slate. This rock, like the by Werner, is to be understood a rock consisting preceding, is compound, and composed essen- of a basis or ground of some compact mineral, tially of quartz and mica. Like gneiss it is slaty, and in this ground are interspersed crystals of but it differs from that rock in containing no some other mineral. The ground or basis varies, felspar. It is always stratified. It very fre- in different porphyries. Sometimes it is clayquently contains garnet crystals in considerable stone, sometimes pitch-stone, &c.; and the porquantity, so as to give it a porphyritic appear- phyry is named from this basis. The following
Its structure is then slaty porphyritic. are the species of porphyry that have been deIt sometimes also contains crystals of tourmaline, scribed :--1. Clay porphyry; 2. Horn-stone cyanite, and granatite. Felspar likewise occurs porphyry; 3. Felspar porphyry; 4. Pitch-stone in it occasionally; not, however, as a constituent, porphyry; 5. Sienite porphyry; 6. Obsidian but in kidney-form and irregular masses. Like porphyry; 7. Pearl-stone porphyry. gneiss, it contains many foreign beds (older por- The crystals interspersed through the different phyry, primitive trap, primitive limestone, older bases are commonly felspar, sometimes quartz, serpe itine, and gypsum, occur in it). It is rich and sometimes hornblende and mica; but the in ores; containing beds of magnetic ironstone, last two are uncommon, especially the mica. pyrites, galena, copper pyrites (containing gold), There are two very different formations of porblende, cinnabar, cobalt glance, magnetic pyrites, phyry; the first is found in beds in gneiss, micaand sometimes even native gold. It abounds slate, and clay-slate; whereas the second always also in metalliferous veins.
lies over all these formations. Hence the first is 4. Clay-slate.—Mica-slate gradually passes distinguished by the name of older, and the into clay-slate, the formation immediately over second is called newer porphyry. It is the first it. Clay-slate consists essentially of the mineral of these that we are to consider at present. described in the preceding chapter under that The basis of the older porphyry is usually a name. This rock is always slaty and always species of horn-stone, and sometimes felspar; stratified. When it approaches mica-slate, and the crystals which occur in it are felspar grains of quartz, and also of mica, may be dis- and quartz. Hence the older porphyry consists tinguished in it. Occasionally also it contains chiefly of horn-stone porphyry, and felspar porcrystals of felspar, schorl, tourmaline, garnet, phyry. When not covered by other formations and hornblende.
it sometimes forms single rocks, but never large Under the name of clay-slate formation are mountains. included not only clay-slate, strictly so called, 6. Primitive trap.— The word trap is Swedish, but likewise chlorite-slate, talc-slate, whet-slate, and signifies a stair. It was applied by the Swe drawing-slate, and alum-slate; all of which dish mineralogists to certain rocks, whose strata occur along with pure clay-slate, are similarly when exposed, from the one jutting out under stratified, and gradually pass into it and into the other, gave an appearance somewhat like a each other, and therefore are considered as only stair. The term was adopted by other nations, constituting a part of the same formation : but and was applied indiscriminately to a great these substances affect a particular order. The variety of rocks, which bore a certain resemfollowing table exhibits that order, beginning blance to each other. This generalisation introwith the lowest or oldest, as it is called, and ter- duced much confusion into the subject, which minating with the uppermost or newest:- was first cleared up by Werner and his disciples. 1. Light yellowish gray clay-slate.
Under the term traps Werner comprehends cer
tain series of rocks, distinguished chiefly by the 2. Dark gray clay-slate. 3. Green clay-slate.
hornblende, which they all contain. In the most
ancient, the hornblende is almost pure; this 4. Chlorite slate and potstone.
purity gradually diminishes, and in the most recent 5. Talc slate.
traps the hornblende degenerates to a kind of in6. Whet slate. 7. Bluish gray clay-slate.
durated clay. There are, then, three formations 8. Red clay-slate.
of trap : 1. Primitive trap; 2. Transition trap;
3. Flætz trap. The first only occupies our at9. Drawing slate.
tention at present. 10. Alum slate.
The primitive trap formation contains a conBesides these different beds, which are con- siderable number of rocks; which, occurring in sidered as constituting the clay-slate formation, different parts of the earth in similar situations, it contains also beds of all the eight subordi- and as it were substituted for each other, are con
sidered altogether as constituting only one for- 7. Primitive limestone.—Limestone occurs mation. The following table exhibits a list of in all the four grand classes of formations, but the rocks belonging to this formation:
it assumes a peculiar and characteristic appcarI. Hornblende.
ance in each. In the primitive it is distinctly 1. Granular or common hornblende.
crystalline and transparent. The crystalline 2. Hornblende slate.
texture gradually becomes less and less distinct,
as the formations advance, till at last the limeII. Hornblende and felspar united. stone assumes the appearance of an earthy i. Granular.
deposite. 1. Common green-stone.
Primitive limestone occurs usually in beds, 2. Porphyritic green-stone.
and seldom forms entire mountains. Its color 3. Green-stone porphyry.
is usually white, sometimes it is gray, but very 4. Green porphyry.
seldom assumes any other color. It is the ii. Siaty
species of limestone described already under the 1. Green-stone slate.
name of granular foliated. It sometimes conIII. Hornblende and mica united. tains in it quartz, mica, hornblende, actilonite, 1. Porphyritic trap.
garnet, tremolite, talc, clay-slate, serpentine,
asbestus, blende, galena, common and magnetic The first two of these rocks consist essentially pyrites, and inagnetic ironstone. The ores are of the minerals described under the names of usually found at the lower part of the beds of common hornblende and bornblende slate. The limestone. It is sometimes stratified, and somelatter sometimes passes into fine slaty gneiss and times not. When not covered by any other into chlorite slate.
formation, it forms steep bare rocks; and, when Common green-stone is coinposed of horn- it occurs in considerable quantities, often conblende and felspar, both in the state of grains or
tains caverns. small crystals, and the hornblende usually con- 8. Older serpentine.—The serpentine formastitutes by far the greatest proportion of the tion consists essentially of the mineral described mass. The felspar is almost always tinged green already under that name. Two subspecies were from the hornblende. This rock sometimes thus described; namely, the common and precious contains a little mica; sometimes it is intersected serpentine. The latter (at least chiefly) constiby small veins of quartz and actinolite; and tutes the formation at present to be described. sometimes also, though less frequently, of felspar It occurs, like the other subordinate primitive and calcareous spar.
formations, in beds in gneiss, mica, and clayPorphyritic green-stone, like the preceding slate, and alternates with limestone. It is seldom rock, is a compound of granular hornblende and stratified. It contains in it galena, and auriferfelspar; but it contains likewise large crystals of ous arsenic pyrites. felspar and quartz, interspersed through the green- 9. Quartz occurs in beds, and in no great stone ground.
quantity. It is usually granular and of a white Green-stone porphyry (black porphyry of the color; sometimes it contains a mixture of mica, antiquary) is a rock consisting of granular green- which gives it a slaty texture. It is very often stone, so small grained that at first sight it has unstratified; but, as it abounds in rents, these the appearance of being a simple stone; con- have often been mistaken for strata. taining in it large crystals of felspar, colored 10. Topaa rock.—The rock which constitutes green from hornblende.
this formation is very rare, having been observed Green porphyry (the verde antico serpentine) only in Saxony, where it constitutes a mountain. is a rock which has for its ground a mixture of There it rests on gneiss, and is covered by clayhornblende and felspar, so intimate that the two slate. It is composed of three ingredients; ingredients cannot be distinguished by the naked namely, fine granular quartz, schorl in thin eye, and having a blackish green or pistacinio prismatic distinct concretions, and topaz almost green color. This trap contains greenish colo- massive. These are arranged in thin layers, and red feispar crystals, often cruciform.
these again are divided into roundish and granuGreen-stone slate is a rock composed of horn- lar distinct concretions, so that the rock is slaty blende and felspar, and sometimes a little mica, granular. The intervals between these concreand having a slaty texture. It is very hard, but, tions are filled up with a yellowish or greenish like the other species of greenstone, soon withers colored lithomarge. when exposed to the air.
11. Gypsum was formerly believed to be Porphyritic trap is a rock composed of an peculiar to the flætz formations; but an immense intimate mixture of hornblende and felspar, con- bed of it has lately been discovered in Switzertaining in it large plates of mica, which give it land in mica-slate. This primitive gypsum a porphyritic appearance.
is characterised by containing mica and clayAll the rocks of the primitive trap formation slate. are characterised by containing a mixture of iron 12. Primitive flint slate.—This rock consists pyrites. Their stratification is indistinct; and, essentially of the mineral, described already indeed, if we except green-stone slate and horn- under the name of flint slate. It is often trablende slate, usually not perceptible. When versed by veins of quartz. There are two forprimitive trap is not covered by any other for- mations of it; namely, the primitive, which mation, it constitutes considerable hills and occurs in beds in clay-slate, and another which cliffs. It abounds in ores, especially green-stone belongs to the transition formations. slate.
Having now described the eight formations
which are subordinate to gneiss, mica, and clay- been formed when the earth was passing from an slates, let us proceed to the remaining primitive uninhabited to an inhabited state. formations, which always cover clay-slate, and 1. Greywacke.—This formation consists of are therefore considered as uewer than it. These two different rocks, which usually alternate with are the newer primitive porphyry, sienite, and each other, and pass into each other. These are the newer serpentine.
greywacke and greywacke slate. The first cha13. Newer Porphyry. To this formation racterises the formation. Greywacke is a rock belong the following species of porphyry; namely, composed of pieces of quartz, flint slate, felspar, clay porphyry, pitchstone porphyry, obsidian and clay-slate, cemented together .by a basis of porphyry, pearlstone porphyry, and sometimes clay-slate. The pieces are sometimes as large félspar porphyry. Clay porphyry is by far the as a hen's egg ; sometimes so small that they most common. To this formation also belongs cannot be perceived by the naked eye. The claystone, a mineral already described. It con- clay-slate basis likewise varies in quantity constitutes the basis of clay porphyry, and frequently siderably. It often contains soft plates of mica, occurs without any crystals of felspar or quartz. and quartz veins are very common in it; someTo it we must also refer a kind of breccia por- times it is so hard that it appears indurated by phyry, composed chiefly of fragments of horn- some siliceous cement. The texture of greystone porphyry and felspar porphyry.
wacke becomes gradually finer and finer grained, 14. Sienite.—This rock occurs usually along till at last it can no longer be perceived, and a with porphyry; and, when they are both together, slaty structure succeeds. It then passes into the sienite generally forms the uppermost part greywacke slate. of the hill.
Greywacke slate is in fact a variety of claySienite is a rock composed essentially of fel- slate; distinguished from primitive slate by selspar and hornblende, the same constituents which dom showing a greenish or light yellowish grey form green-stone; but in sienite the felspar is color, or the silvery uninterrupted lustre of prithe prevailing ingredient, whereas in green-stone mitive slate. It contains no beds of quartz, but it is the hornblende. In sienite the felspar is very often veins of that mineral; no crystals of . usually red, and very seldom has a tinge of green, felspar, schorl, tourmaline, garnet, or hornwhereas in green-stone the felspar is never red, blende; nor beds of garnet, chlorite slate, talc, but almost always greenish white. The structure or magnetic ironstone. It contains petrifaction of sienite is granular, and the grains vary greatly The greywacke rocks are stratified. 'It contains in size; sometimes small grained sienite contains immense beds of transition limestone, trap, and in it large crystals of felspar; it is then called flint slate; and is rich in ores both in beds and porphyritic sienite. When the two ingredients veins, and the veins are often of an uncommonly that constitute sienite are so small, and so inti- large size. mately mixed, that they cannot be distinguished 2. Transition limestone. This, like primitive by the naked eye, and when such a rock contains limestone, is a simple rock; but it approaches crystals of felspar and quartz, it is denominated more to compact, and is less transparent than sienite porphyry.
the primitive. It contains often veins of calcaSienite, like porphyry, contains few foreign reous spar, and exhibits a variety of colors, beds : but it is rich in ores, containing gold, which give it a marbled appearance. It consilver, iron, tin, copper, lead, &c., always how- tains marine petrifactions of corals and zooever in veins.
phytes, which no longer exist, and which do not The rocks of sienite are often divided into occur in the subsequent limestone formations. columns. Like the newer porphyry it often These petrifactions increase in quantity as the occurs in round masses.
beds of transition limestone advance farther and 15. Newer serpentine.—This forination consists farther in their position from the primitive forof the rock composed essentially of the mineral mations. It is often mixed with greywacke called common serpentine. It bears a striking slate, which gives it a slaty texture. It occurs resemblance to the newer porphyry formation, in beds of greater and smaller size, and often and occurs in similar situations.
forms whole mountains. It contains no foreign Class II.-TRANSITION FORMATIONS.
beds except of transition trap. It is scarcely
stratified. It is rich in ores. Having described the primitive formations, let 3. Transition traps.—This formation, as the us now proceed to the second great class, the name imports, consists of rocks distinguished transition, which lie immediately over them, by the great proportion of hornblende which These are by no means so numerous, since they they contain. "It comprehends four species of consist only of four sets; namely, 1. Greywacke; rocks; namely, 1. Transition greenstone. 2. 2. Transition limestone; 3. Transition trap; Amygdaloid. 3. Porphyritic transition trap. 4. Transition flint-slate. They all alternate with 4. Globular trap (kugel fels). each other.
Transition greenstone is a rock composed of It is in the transition rocks that petrifactions fine granular hornblende and felspar intimately first make their appearance; and it deserves mixed together, and not so distinctly crystallised particular attention that they always consist of as in primitive greenstone. Sometimes the mixspecies of corals and zoophytes, which do not ture is so intimate that the two minerals cannot at present exist, and which therefore we must be distinguished. In that state it often becomes suppose extinct.
The name transition has loose in its texture, and approaches wacke and been imposed, as they are supposed to have basalt. In this last case it often contains vesi