globe, and so arrive at that which is the aim and object of all true geological research. EXPLANATORY NOTE. PETRIFACTIONS are, in general, described according to the mineral substance which enters most abundantly into their composition. If it be lime, then they are designated calcareous (Lat., calx, lime); if flint, siliceous or silicified (silex, flint); and so on of other minerals. BITUMEN (Gr., pitus, the pitch tree)-a variety of inflammable mineral substances, which, like pitch, burn with flame in the open air. Naphtha, petroleum, and asphaltum, are familiar examples; and all substances impregnated with these bitumens are said to be bituminous. As mentioned in the text, it is the prevalent opinion that all bituminous matter is of organic or vegetable origin. BITUMINOUS FERMENTATION.-All vegetable matter is liable to certain states of fermentation, according to the degree of heat, air, and moisture to which it is subjected. These states have been successively described as the saccharine, vinous, acetous, septic, and bituminous. For example, the saccharine is that which manifests itself in the operation of malting and in the ripening of fruits; if water and heat be applied, it passes into the vinous, or that by which wine and spirituous liquors are formed, Again, if, while the vinous is going on, air be partially admitted, the acetous, or vinegar-forming fermentation, will be produced; and by further exposure of the vegetable matter to the air, it will pass into a mass of earth and carbon: this fits it for the septic, or putrefying process; but if air be excluded, and heat, moisture, and pressure be present, the bituminous will be the result. By a knowledge of these processes, it is easy to understand how malt, wine, vinegar, vegetable mould, and coal, are respectively formed. ADIPOCERE (Lat., adeps, fat, cera, wax)—a fatty substance produced by the decomposition of the flesh of animals in moist situations, or under water, resembling, in some of its properties, a mixture of fat and wax. It is found in damp grave-yards, in peat-bogs where animals have been accidentally entombed, and is also occasionally thrown up on the sea-shore after a storm. It has a chalky aspect, a soapy feel, is inflammable, and swims in water. FOSSIL BOTANY AND ZOOLOGY.-The animals peculiar to a country constitute its Fauna, and the plants its Flora. The terms are respectively derived from the Latin Fauni, rural deities, and Flora, the goddess of flowers. As naturalists speak of the existing Fauna and Flora of any country, so geologists speak of the fossil Fauna and fossil Flora of certain geological epochs and formations. CLASSIFICATION OF ROCK FORMATIONS. 124. The subjects treated in the preceding sections may be regarded as introductory to the study of Descriptive Geology; for, without a knowledge of them, it would be impossible to comprehend the nature of the changes which our planet has hitherto undergone. Those changes are indicated by certain characters stamped upon the rocks which constitute its crust -characters obviously analogous to such as are now produced by causes in active operation around us. It was necessary, therefore, to learn something of the existing structure and conditions of the globe, and of the causes-mechanical, chemical, and vital—which are modifying these conditions, in order that we might be enabled to reason from what is recent and apparent, to that which has taken place at more remote periods. 125. The term rock is applied by geologists not only to those hard substances usually called so, but also to all sands, clays, gravels, and marls which occur in beds, strata, or masses. It is also used to denote a collection of such substances: thus, we say the "rocks of a country;" or, speaking more definitely of any mineral series, we say the Chalk rocks, the Carboniferous rocks, and so on. The rocks which compose the crust of the earth, though varying much in mineral character, as well as external appearance, occur either in masses, or in series having a close resemblance to each other; so much so, that geologists conclude that certain series have been formed under similar circumstances. This opinion is further confirmed by the fact, that certain series of strata always imbed fossils of a different character from those contained in any other series; hence the origin of rock classification. 126. Leibnitz, in 1680, divided rocks into two great classes— STRATIFIED and UNSTRATIFIED-the latter being the result of igneous fusion, and the former that of aqueous solution. This distinction, though of importance at the period to which we refer, was still of little avail in deciphering the history of the earth, as unstratified rocks are mingled with the highest as well as with the lowest strata; and as, moreover, the stratified rocks differ essentially from each other, and often contain very different fossil remains. Lehman, a German mineralogist, next proposed to divide the stratified rocks into PRIMITIVE-those containing no fossil organic remains. SECONDARY-those containing remains of animals and vegetables. LOCAL-those but partially occurring in different districts. 127. Werner, the great German geologist, improved upon this classification, and divided all rocks into Primary, Transition, Secondary, and Local. The term Transition was added by Werner, as implying that the rocks so called exhibited a passage from the primary into the secondary in regard to their mineral character, and also that the earth was changing from an uninhabitable to an inhabitable state during the period of their formation. Subsequently, from the fossil discoveries of Cuvier and others, a more definite idea was attached to the term Local, and the word Tertiary was E employed to denote all those regularly stratified beds which FORMATIONS. (SUPERFICIAL ACCUMULATIONS-all loose and irregularly deposited TERTIARY-local deposits of regular strata, containing remains of SECONDARY-strata of chalk, clay, and shale, red and white sand- TRANSITION-strata of sandstones, shales, slates, and limestones--- PRIMARY-slaty and crystalline strata, very hard and compact, 128. As geologists became better acquainted with the suc- alluvial 200 feet/Tertiary 2000ft/ Secondary 5000 Palaeraic 33,000 Crystalline TABLE OF BRITISH DEPOSITS. Unstratified SOIL-decomposed vegetable and animal matter, with earthy admixtures. 2000 ft Tertiary Pentersic SUPERFICIAL Elevation of th Gertiary period TERTIARY. ALLUVIUM-deposits of sand, gravel, and clay, DILUVIUM-deposits of gravel and clay with FRESH-WATER, OR ESTUARY BEDS-consisting of MARINE BEDS-consisting of blue and plastic clays, thin beds of sand, lignite, &c. Characteristie = prevalences of Vernesinal Mammalia. Characteristic. SECONDARY FORMATION. Chalk CLASSIFICATION OF ROCK FORMATIONS. System. 67 CHALK-soft and white, with layers of flint; chalk, hard, and without flints. GAULT, or beds of bluish marly clays, with green 2400ft Tarasoic' WEALDEN GROUP-beds of clay, argillaceous lime RED SANDSTONE GROUP-fine-grained, sometimes MAGNESIAN LIMESTONE-thick-bedded limestones COAL MEASURES-alternating beds of coal, shale, thick-bedded Carboniferous CARBONIFEROUS, OR MOUNTAIN LIMESTONE-thick- Old Red System. RED SANDSTONES-sometimes fine-grained, some- ཎ9༠༠f་ Triassic 33000 fer Prolazoic Silurian TRANSITION. PRIMARY. Silurian Grauwacke Clay-Slate Mica Schist Gneiss UPPER SILURIAN rocks-gray and bluish limestones, LOWER SILURIAN rocks-impure shelly limestone, CLAY-SLATE-finely laminated; dark, liver, and pur- HORNBLENDE AND CHIASTOLITE slates, finely lami- CHLORITE SLATES-greenish-coloured slates, with GNEISS ROCKS-intermingled with irregular beds Grande, Porphyry, Trop oc To assist the student in forming an idea of the succession of these formations and systems, the stratified rocks are more summarily arranged in the following diagram: * From Triple series of Diary, Timestone & Sandstoner. |