ROCK. 
R. cuneala, and R. ovata, both natives of 
Jamaica. 
ROCK, a stony mass, forming a portion 
of the substance of this globe. Rocks are 
in general disposed in raountanic ranges; 
but in some few instances are found existing 
in immensely large separate masses. 
The obvious ditferences existing in the 
appearances and composition of ditferent 
rocks and mountains have long induced 
mineralogists to consider them as formed at 
very distant periods from each other, and 
even to suppose, that those of the later for- 
mation frequently derived the materials of 
which they were composed, from the disin- 
tegration of the previously existing, and 
much more ancient rocks. Hence arose 
their division into primeval, or primitive ; 
and secondary, or epizootic ; and in conse- 
quence of the prevalence of the opinion of 
the primitive rocks supplying the materials 
of those of secondary formation, the latter 
were further separated into original and 
derivative. The secondary rocks were also 
considered as otherwise differing in their 
origin ; some being supposed to be marige- 
nous, and others alluvial. 
The celebrated Werner considers all 
rocks, with respect to their origin, to be 
aquatic or ignigenous. The aquatic are 
divided, agreeable to the period, and the 
particular mode of their formation, into, 
i. Primitive, being chemical precipitates, 
bearing no traces of organised beings, and 
formed in the early chaotic state of the 
earth. 2. Transition, formed, as the term 
implies,, during the transition of the earth 
into a habitable state. 3. Floetz rocks, dis- 
posed in flat or horizontal strata, after the 
creation of animals and vegetables ; the re- 
mains of which are often found in the sub- 
stance of these rocks : as the primitive are 
of purely chemical, so flip two latter are 
of partly chemical, and partly mechanical 
formation. 4. Alluvial, formed by the 
component parts of previously existing 
rocks, separated by the influence of air, 
water, and change of temperature, and de- 
posited in beds. 5. Volcanic rocks, which, 
according to their originating from true vol- 
canoes, or from pseudo-volcanoes, are con- 
sidered as volcanic, or pseudo-volcanic. 
Mountain rocks are simple, as when 
formed of limestone, clay-slate, serpentine, 
or any other simple fossil ; and compound, 
when formed by the aggregations of simple 
fossils. The compound rocks are either 
cemented, formed of various parts brought 
together and connected by a cement, as in 
sand-stones, pudding-stones, and breccias; 
or are aggregated, being composed of parts 
existing originally on the spot where the 
masses are now found, and connected toge- 
ther by their original structure. They are 
also considered as simple aggregated, when 
one, as a base includes the other; when 
the contained portion is in the form of 
grains or crystals, the structure is termed 
porphyritic ; and when of a vesicular form, 
amygdaloidal : the double aggregated is 
when a smaller structure is contained in a 
larger, as granular slaty ; or when the two 
structures exist near or beside each other ; 
when the one not including the other is 
pointed out by a conjunction, as porphyri- 
tic and amygdaloidal. 
The mountain masses themselves are 
either of a stratified or of a seamed struc- 
ture. When thcv masses composing the 
rock are of one species, and disposed pa- 
rallel to each other, those masses are termed 
strata; but when the mountain mass is 
composed of different species of rocks ; thus 
disposed, it is said to be formed of beds. 
In the seamed structure, the seams of stra- 
tification, though parallel in one direction, 
intersect each other in another. The masses 
thus . divided by these intersecting seams, 
may be considered as distinct concretions, 
and may be instanced in the columnar 
formed. Straight and much thicker masses 
are also thus formed, by what is termed the 
tabular seamed structure, and large globu- 
lar masses result from the large globular or 
massive structure. 
By a rock formation, Mr. Jameson un- 
derstands “ a determinate assemblage of 
similar or dissimilar rock masses, which 
are characterised by external and internal 
relations, as an independent whole, that is, 
as an unity in the series of rock formations.” 
When the mass is uniform throughout, it 
constitutes a simple formation ; but when 
dissimilar, a compound formation ; and when 
these formations are repeated, the whole is 
denominated a series or suite of formations. 
When individual beds occur in different 
principal formations, as primitive trap in 
gneiss, mica-slate, &c. forming single inde- 
pendent wholes, which always continue the 
same, notwithstanding the difference of 
rocks in which they are imbedded, and 
still form members of a series of formations ; 
they are considered as independent forma- 
tions. The inclination of a stratum is the 
angle which the stratum forms wifli the ho- 
rizon, and is determined by the quadrant. 
The dip is the point of the compass to- 
