fnd of a red or green colour. The crystals 
are quartz and felspar. 
2. Felspar porphyry. The ground is usu- 
ally red. The cry stals are felspar and quartz. 
3. Sienite porphyry. The ground is a 
mixture of felspar and hornblende. The 
crystals are felspar and quartz. 
4. Pitchstone porphyry. The ground is 
red or green, sometimes brown, and even 
black. 
5. Clay porphyry. The ground is an in- 
durated clay, commonly reddish, which 
sometimes passes into splintery hornstone. 
The crystals are felspar and quartz ; some- 
times it contains- hornblende, and more rare- 
ly mica. 
Porphyry mountains are not stratified, and 
contain no beds of foreign substances. They 
are not rich in ores, yet frequently contain 
veins worth working. * 
Sienite. This rock is composed essentially 
of crystals of felspar and hornblende, imme- 
diately and intimately united. The felspar 
usually predominates. When the felspar is 
compact, the rock assumes a porphyritic 
structure. ,lt sometimes contains accidentally 
grains of quartz and mica, but in a very 
small proportion. Its texture is granular, 
rarely shistose. Seldom stratified. Does 
not contain foreign bed'. It sometimes con- 
tains metallic veins. It usually covers por- 
phyry. 
Serpentine. This rock is essentially simple. 
Sometimes it contains accidentally talc, as- 
bestus, and steatites ; and sometimes mica, 
garnets, and granular limestone, magnetic 
ironstone, arsenical pyrites, &c. Serpentine 
rocks are not stratified. Seldom contain 
beds of foreign minerals. They contain few 
ores, and seldom any worth working. 
Primitive limestone. This rock is essen- 
tially simple : its mass is granular limestone 
of a greyish white colour. Sometimes it is 
accidentally mixed with mica, quartz, horn- 
blende, tremolite, aetinote, asbestos, talc, 
&c. Its texture granular, the grains have a 
foliated texture, and a crystallized appear- 
ance. This rock sometimes contains metal- 
lic veins; chiefly of galena, magnetic iron- 
stone, blende, and pyrites. 
Primitive traps. The word trap is Swed- 
ish, and signifies a stair. It was applied by 
the Swedish mineralogists to certain rocks 
whose strata when exposed, the one jutting 
out under the other, gave an appearance 
somewhat like a stair. The term was adopt- 
ed by other nations, and was applied indis- 
criminately to a great variety of rocks ; 
which yet bore a certain resemblance to each 
other. This generalization, however, int o- 
dueed much confusion into the subject, which 
was first cleared up by Werner and ins dis- 
ciples. Under the term traps Werner com- 
prehends certain series of rocks, distinguished 
chiefly by the hornblende, which they all 
contain, in the most antient, the hornblende 
is almost pure; this purity gradually di- 
minishes, and in the most recent traps the 
hornb'endedegenerates to a kind of indurat- 
ed day. There are, then, three formations 
of traps; 1. Primitive traps; 2. Transition 
traps ; 3. Secondary traps. The first only 
occupy our attention at present. 
The primitive traps are composed almost 
entirely of hornblende. It is sometimes mixed 
with felspar, more rarely with mica and py- 
rites, There are four species ; 1. Common 
ROCKS. 
599 
hornblende ; 2. Shistose hornblende ; 3. Pri- 
mitive grunstein ; 4. Shistose grunstein. 
1 . Common hornblende is a simple rock. 
Its grains are sometimes so small that it ap- i 
pears compact. Sometimes it contains mica. 
2. Shistose hornblende occasionally con- j 
tains quartz, aetinote, and pyrites. 
3. Primitive grunstein is a mixture of 
hornblende and felspar. It is divided into 
different varieties, according as its texture is 
granular or compact. 1st. Common grun- 
stein, in which the hornblende and felspar 
are intimately united. It resembles a sien- 
ite, in which the hornblende predominates. 
2d. Fine grained grunstein, in which are em- 
bedded crystals of felspar. Texture at once 
granular and porphyritic. 3d. When the 
grains become very fine, the grunstein be- 
comes porphyritic. 4th. When the mass be- 
comes entirely homogeneous, we have the 
green porphyry of the antients. 
4. Shistose grunstein is a rock composed 
of compact felspar, hornblende, and a little | 
mica; sometimes it contains also quartz. 
Its texture is shistose. The hornblende and 
felspar occur nearly in equal proportion. 
Grunstein often contains metallic veins, 
Quartz. Considerable rocks occur com- 
posed entirely of quartz. Sometimes, in- i 
deed, they contain accidentally mica, felspar, j 
tin, pyrites. The texture of these rocks is j 
usually compact, but sometimes shistose. 
Topasfds. dins rock -is composed of quartz, j 
shod, topaz, and lilhomarga. d he first ; 
three ingredients alternate in thin beds. Its j 
texture is granular ; its structure shistose. j 
Very rare. It has been found only in Saxony, j 
near Awerbach, forming a mountain called j 
Schneckcnstein. It rests upon granite, and j 
contains no ores. 
Kieselchiefer. Kieselchiefer, or siliceous ! 
shistus, often forms considerable rocks. ■ 
1 heir texture is compact. They are often 1 
traversed by small veins of quartz, They 
contain no metallic substance. 
Rocks of transition. 
ddie rocks belonging to this class agree 
with those of the first in containing no re- 
mains of organized beings, or at least but 
seldom ; but they have a considerable re- 
semblance to those of the third class. Wer- 
ner considers them as forming the passage be- 
tween the first and third class of rocks; • 
hence their name. The following table con- 
tains a list of the transition rocks. 
1. Transition limestone, 
2. Grauvvacke, 
3. Transition traps, 
Let us take a view of each of these in 
order. 
Transition limestone. This rock is simple. 
Its mass is a limestone ; sometimes granular, 
sometimes compact, according as its age ap- 
proaches to primitive or secondary limestone. 
Fracture is somewhat splintery. Somewhat 
transparent. Its colours are variously ming- 
led ; often red or black with white veins. 
Seldom contains foreign substances. Some- 
times shells are observed in its superior strata.. 
Sometimes it alternates with beds of argil- 
laceous shistus, and sometimes with beds of 
mandelstein, as in Derbyshire. It usually 
covers argillaceous shistus. Seldom rises to 
any considerable height. Usually stratified. 
Strata very thick. Often contains metallic 
veins. 
Graurvacke. There are two species of 
rocks of grauwaeke, common and shistose. 
Common grauwaeke is a sandstone com- 
posed of grains of quartz, kieselchiefer, and 
■argillaceous shistus agglutinated by a cement 
of clay. The grains are sometimes very 
small, sometimes as large as a hazel nut. 
Shistose grauwaeke is a simple shistose 
rock, which has a strong resemblance to ar- 
gillaceous shistus, but differing in its position. 
It forms beds which alternate w ith common 
grauwaeke. 
Grauwaeke rocks are traversed by veins 
of quartz. They contain sometimes shells 
and reeds petrified. They contain no foreign 
beds. These rocks are distinctly stratified. 
T he strata do not run parallel to {hose of the 
other rocks on which they lie. They usually 
cover transition limestone, and do not rise 
to any great height, d'hey are rich in ores. 
Transition traps. The principal base of 
all the rocks belonging to this formation is 
grunstein. This constitutes many of the 
primitive traps; but in the transition traps, 
the mixture h much vn-ore intimate, the 
grain is much finer, and the mass much more 
homogeneous, and its constituents are more 
or less blended together. Transition traps 
consist principally of two species^ mandelstein 
and globular trap. 
1. Mandelstein or amygdaloid. By this 
term is implied all rocks composed of a com - 
pact ground, containing imbedded in it mi- 
nerals of a round or almond for nr, or con- 
taining cavities of that form, d’hey are dis- 
tinguished into primitive, transition, and se- 
condary mandel'steins. Transition maud el- 
stein consists of a ground of shistose horn- 
blende, decomposed and resembling wacken 
or ferruginous clay. The cavities are some- 
times empty, sometimes full, and then they 
contain quartz and chalcedony. T he. toad- 
stone of Derbyshire is referred to this spee- 
ch's. It contains round masses of calcareous 
spar. 
2. Globular trap. This is a shistose gran- 
stein, partly decomposed and reduced to the 
state of a tine grained wacken. It is com- 
posed of large spherical bodies, consisting of 
concentric layers; the central part beinsc 
hardest. 
Transition traps .are not stratified. They 
form separate conical mountains, usually near 
those of transition limestone. They contain 
some metallic veins of copper, iron, tin, &c:. 
class m. 
Rocks secondare. 
These rocks are distinguished by the re- 
mains of organized bodies, which they’ con- 
tain abundantly. They are usually stratified. 
The follow ing table contains a list of these- 
different rocks, arranged according to the- 
supposed time of their formation, 
1. Sandstone,. 5. llock salt,. 
2. Secondary lime- 6. Pit coal, 
stone, 7. Eisenthon, 
3. Chalk, S. Secondary traps. 
4. Gypsum, 
Sandstone. This rock is composed cf 
quartz, varying- in size ; sometimes also grains 
of kieselschiefer, and very rarely of felspar. 
These grains are cemented together, some- 
times by means of clay, sometimes of marl 
or lime, and sometimes of quartz. The ce- 
ment varies in quantity, but never predoiai- 
