ROCHEFORTIA, in botany, so nam ed in memory of De Rochefort, a genus of the Pentandria Digynia class and or der. Natural order of Dumosm. Rham ni, Jussieu. Essential character : calyx five-parted; corolla one petalled, fun nel-form, inferior, with the aperture open ; fruit two-celled, many-seeded.
There are two species, viz. R. euneala, and R. ovata, both natives of Jamaica. ROCK, a stony mass, forming a por tion of the substance of this globe. Rocks are in general disposed in moon tanic ranges ; but in some few instances are found existing in immensely large separate masses.
The obvious differences existing in the appearances and composition of different 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 lat ter tbrmation frequently derived the ma terials of which they were composed from the disintegration of the previously existing and much more ancient rocks. Hence arose their division into primeval, or primitive : and secondary, or epizootic; and in consequence of the prevalence of the opinion of the primitive rocks supply ing the materials of those of secondary formation, the latter were further separa ted into original and derivative. The secondary rocks were also considered as otherwise differing in their origin ; some being supposed to be rnarigenous, 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, 1. Primitive, being chemical precipitates, bearing no traces of organized 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, disposed in flat or horizontal stra ta, after the creation of animals and vege tables ; the remains of which are often found in the substance of these rocks : as the primitive are of purely chemical, so the two latter are of partly chemical, and partly mechanical formation. 4. Al
luvial, formed by the component parts of previously existing rocks, separated by the influence of air, water, and change of temperature, and deposited in beds. 5. Volcanic rocks, which, according to their originating from true volcanoes, or from pseudo-volcanoes, are considered as vol canic, or pseudo-volcanic.
Mountain rocks are simple, as when formed of limestone, clay-slate, serpen tine, or any other simple fossil ; and com pound, 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 breccix ; or are aggregated, being composed of parts existing original ly on the spot wbere the masses are now found, and connected together by their original structure. They are also consi• dered as simple aggregated, when one, as a base, includes the other ; when the con tained portion is in the form of grains or crystals, the structure is termed porphy ride ; and when of a vesicular form, amyg daloidal : the double aggregated is when a smaller structure is contained in a larg er, 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 porphy ride and amygdaloidal.
The mountain masses themselves are either of a stratified or of a seamed struc ture. When the 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 rucks, thus disposed, it is said to be formed of beds. In the seamed struc ture, the seams of stratification, though parallel in one direction, intersect each other in another. The masses thus divid ed 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 globular masses result from the large globular or massive structure.