HEMIPTERA. An order of insects, so called from a peculiarity in their wings, the superior being coriaceous at the base and membranous at the apex, ??s?, _hemisu_, half, and pte???, _pteron_, wing.

HORNBLENDE. A simple mineral of a dark green or black color, which enters largely into the composition of several varieties of the Trap-Rocks.

HORNSTONE. A siliceous mineral substance, sometimes approaching nearly to flint, or common quartz. It has a conchoidal fracture, and is infusible, which distinguishes it from compact felspar.

HUMERUS. The bone of the upper arm.

HYDROPHYTES. Plants which grow in water. _Etym._, ?d??, _hydor_, water, and f?t??, _phyton_, plant.

HYPOGENE ROCKS. Those rocks which are _nether-formed_, or which have not a.s.sumed their present form and structure at the surface, such as granite, gneiss, &c. The term, which includes both the plutonic and metamorphic rocks, is subst.i.tuted for _primary_, because some members of both these cla.s.ses, such as granite and gneiss, are posterior to many secondary or fossiliferous rocks. _Etym._, ?p?, _hypo_, under, and ????a?, _ginomai_, to be formed or produced.

ICEBERG. Great ma.s.ses of ice, often the size of hills, which float in the polar and adjacent seas. _Etym._, ice, and _berg_, German for hill.

ICHTHYOSAURUS. A gigantic fossil marine reptile, allied in part of its structure to a fish. _Etym._, ?????, _ichthus_, a fish, and sa??a, _saura_, a lizard.

IGNEOUS ROCKS. All rocks, such as lava, trap, and granite, known or supposed to have been melted by volcanic heat.

INCANDESCENT. White hot--having a more intense degree of heat than red heat.

INDUCTION. A consequence, inference, or general principle drawn from a number of particular facts or phenomena. The inductive philosophy, says Mr. Whewell, has been rightly described as a science which ascends from particular facts to general principles, and then descends again from these general principles to particular applications.

INFUSORY ANIMALCULES. Minute living creatures found in many _infusions_; and the term _infusori_ has been given to all such animalcules, whether found in infusions or in stagnant water, vinegar, &c.

INSp.i.s.sATED. Thickened. _Etym._, _sp.i.s.sus_, thick.

INVERTEBRATED ANIMALS. Animals which are not furnished with a back-bone. For a further explanation, see "Vertebrated Animals."

ISOTHERMAL. Such zones or divisions of the land, ocean, or atmosphere, which have an equal degree of mean annual warmth, are said to be isothermal, from ?s??, _isos_, equal, and ?e??, _therme_, heat.

IOINTS. Fissures or lines of parting in rocks, often at right angles to the planes of stratification. The partings which divide columnar basalt into prisms are joints.

IURA LIMESTONE. The limestones belonging to the Oolite Group const.i.tute the chief part of the mountains of Jura between France and Switzerland; and hence the geologists of the Continent have given the name to the group.

KEUPER. A German name for a member of the Upper New Red Sandstone.

KIMMERIDGE CLAY. A thick bed of clay, const.i.tuting a member of the Oolite Group. So called because it is found well developed at Kimmeridge, in the Isle of Purbeck, Dorsetshire.

LACUSTRINE. Belonging to a lake. _Etym._, _lacus_, a lake.

LAMANTINE. A living species of the herbivorous Cetacea or whale tribe which inhabits the mouth of rivers on the coasts of Africa and South America: the sea-cow.

LAMELLIFEROUS. Having a structure consisting of thin plates or leaves like paper. _Etym._, _lamella_, the diminutive of _lamina_, plate, and _fero_, to bear.

LAMINae. Latin for plates; used in geology for the smaller layers of which a stratum is frequently composed.

LANDSLIP. A portion of land that has slid down in consequence of disturbance by an earthquake, or from being undermined by water washing away the lower beds which supported it.

LAPIDIFICATION. Lapidifying process. Conversion into stone. _Etym._, _lapis_, stone, and _fio_, to make.

LAPILLI. Small volcanic cinders. _Lapillus_, a little stone.

LAVA. The stone which flows in a melted state from a volcano.

LEPIDODENDRON, a genus of fossil plants of the Coal Measures, intermediate in character between the Lycopodiums and coniferous plants.

LEUCITE. A simple mineral found in volcanic rocks, crystallized, and of a white color. _Etym._, ?e?c??, _leucos_, white.

LIAS. A provincial name for an argillaceous limestone, characterized together with its a.s.sociated beds by peculiar fossils, and forming a particular group of strata, interposed between the Oolite and the New Red Sandstone.

LIGNIPERDOUS. A term applied to insects which destroy wood. _Etym._, _lignum_, wood, and _perdo_, to destroy.

LIGNITE. Wood converted into a kind of coal. _Etym._, _lignum_, wood.

LITHODOMI. Molluscous animals which form holes in the solid rocks in which they lodge themselves. The holes are not perforated mechanically, but the rock appears to be dissolved. _Etym._, ?????, _lithos_, stone, and de?, _demo_, to build.

LITHOGENOUS POLYPS. Animals which form coral.

LITHOGRAPHIC STONE. A slaty compact limestone, of a yellowish color and fine grain, used in lithography, which is the art of drawing upon and printing from stone _Etym._, ?????, _lithos_, stone, and ??af?, _grapho_, to write.

LITHOIDAL. Having a stony structure.

LITHOLOGICAL. A term expressing the stony structure or character of a mineral ma.s.s. We speak of the lithological character of a stratum as distinguished from its zoological character. _Etym._, ?????, _lithos_, stone, and ?????, _logos_, discourse.

LITHOPHAGI. Molluscous animals which form holes in solid stones. See "Lithodomi." _Etym._, ?????, _lithos_, stone, and fa?e??, _phagein_, to eat.

LITHOPHITES. The animals which form Stone-coral.

LITTORAL. Belonging to the sh.o.r.e. _Etym._, _littus_, the sh.o.r.e.

LOAM. A mixture of sand and clay.

LOPHIODON. A genus of extinct quadrupeds, allied to the tapir, named from eminences on the teeth.

LYCOPODIACEae. Plants of an inferior degree of organization to Coniferae, some of which they very much resemble in foliage, but all recent species are infinitely smaller. Many of the fossil species are as gigantic as recent Coniferae. Their mode of reproduction is a.n.a.logous to that of ferns. In English they are called club-mosses, generally found in mountainous heaths in the north of England.

LYDIAN STONE. Flinty slate; a kind of quartz or flint, allied to Hornstone, but of a grayish black color.

MACIGNO. In Italy this term has been applied to a siliceous sandstone sometimes containing calcareous grains, mica, &c.

MADREPORE. A genus of corals, but generally applied to all the corals distinguished by superficial star-shaped cavities. There are several fossil species.

MAGNESIAN LIMESTONE. An extensive series of beds, the geological position of which is immediately above the Coal Measures; so called, because the limestone, the princ.i.p.al member of the series, contains much of the earth magnesia as a const.i.tuent part.

MAMMIFEROUS. Mammifers. Animals which give suck to their young. To this cla.s.s all the warm-blooded quadrupeds, and the Cetacea, or whales, belong. _Etym._, _mamma_, a breast, _fero_, to bear.