Mountains are often classified according to their mode of formation: Fold
mountains; Block mountains; Residual mountains; Volcanic mountains.
High mountain chains such as the Himalayas, Andes, Alps, and Rockies are known as new fold mountain systems. The term 'fold' is a reference to the way in which such mountains have been formed. Throughout millions of years slow movements of the earth's crust have caused these
mountains to be raised. The movements which have resulted in mountain buildings were not, however, vertical uplifts. They were primarily horizontal movements, the effect of which was to cause the crust of the earth to 'wrinkle', in a similar way to which a tablecloth wrinkles if it is pushed along the table. The arched or upraised parts of the folds are known as anticlines and the troughs as synclines. These folds can vary greatly in size. Mountain building is undoubtedly due to some deep-seated cause. For a long period the most simple explanation was that folding was entirely due to the cooling and contraction of the earth, so that the crust, already cold and shrunken, had to wrinkle to fit itself to the still cooling and contracting 'core'. One of the objections advanced against this theory is that the amount of shrinking necessary to account for the Himalayas, Alps, etc., seems to be greater than the mere contraction of the earth would allow. While the theory of contraction cannot be completely rejected, serious consideration must be given to the more recent explanations of mountain building. For instance, Wegener suggests that mountain building may be due to the 'wrinkles' produced by the drifting of a continental mass, e.g. that the Alps were formed by the northward drift of the African continent towards the more stable blocks of Central Europe. As the African mass drifted slowly northward the zone between it and the European mass became narrower, and the land was raised into high ridges or folds. The raising of the Alps was accompanied by the formation of the deep trough which contains the Mediterranean Sea. The same hypothesis would account for the building of the Himalayas and the depression of the Indo-Gangetic trough by the northward drift of the Deccan mass.
During the physical history of the earth, mountain building appears to have proceeded more actively at some periods than others. Fold mountains are, therefore, not all of the same age. The newest group of fold mountains include the Himalayas, Alps, Rockies, and Andes. During an earlier period of folding (the Carboniferous) the Pennines, Appalachians, the Cape Ranges of South Africa, and the Dividing Range of Australia were uplifted. A still earlier period of folding accounted for the original mountains of Scotland and Norway, of which the present mountains are merely the worn down stumps. The older fold mountains, which have been subjected to the forces of denudation (such as the weather, rivers, glaciers, etc.) for long geological periods, are much lower and less rugged than the newer fold mountains. The term 'new fold' is applied to the mountain ranges which have been folded most recently, but they seem very old when their age in actual years is considered because they were uplifted many millions of years before historic time. Mountain building is a very long and slow process; and in the case of certain mountain chains, such as the Andes and the mountains of Japan, is probably still proceeding.
The new fold mountain systems of the world, except in such instances as the simple low folds of the Weald (South-east England), usually consist of high parallel ranges, the average height being well over 3000 metres. In the Himalayas' the highest peak rises to 8840 metres; in the Andes 7000 metres; in the Rockies 6000 metres; in the Alps to 4600 metres. Vast though these heights appear, the wrinkles of the earth's crust are only slight. The highest mountain in the world (MountEverest) is about five miles high, so that on a globe of 40 cm, diameter it would protrude only 2.5 mm. Most of the active volcanoes are found in the neighbourhood of fold mountains, where the crust of the earth has been fractured during the process of folding. All around the PacificOcean there are many active and extinct volcanoes, as in New Zealand, the East Indies, Japan, and North, Central, and South America. Another belt of active volcanoes is associated with the fold mountains of the West Indies. The mountains of this type are characterised by ruggedness of relief in contrast to the smooth and rounded contours of mountain areas which have been subjected to weathering agents for long periods of time. This is obvious if pictures of the Alps and the Scottish Highlands are compared.
Mountains are effective climatic barriers, and the climates of regions on either side of a high mountain range are very different. For example, the coast lands of British Columbia have an equable climate and a heavy rainfall, while the lands to the east of the Rockies have an extreme climate and light rainfall. Again, the climate of the mountainous areas differs from that of the adjacent lowlands. The great mountain systems of the world are mainly important for their minerals, and, in the temperate zone, for their lumber. In the plateau regions of some mountain systems agriculture has been made possible by irrigation, and above the forests in temperate areas there are valuable alpine pastures. The swift streams of mountains are frequently sources of hydro-electric power, especially in countries which have no coal, such as Switzerland and Norway. In North America, the Western Cordillera provides gold, copper, lead, and silver, especially in the states of Nevada and Montana. The Andes provide tin and copper (Bolivia), gold and platinum
(Colombia), and silver (Peru). The Highlands of East Australia are important for copper and gold. The lumbering industry is specially important in British Columbia, Washington, and Oregon (soft woods), the Central American mountainous lands (hard woods), the Himalayan slopes (teak and sal), and the Scandinavian mountains (soft woods).
To provide food for the mining communities in inaccessible mountain areas, agriculture has been developed. There are numerous irrigation schemes in operation in most of the mountain states of the USA, e.g. at SaltLake City in Utah. Similarly, the Andean states, e.g. Bolivia, grow small quantities of cereals in the plateau areas. Mountain pastures have been utilised most extensively for cattle rearing in Switzerland and Scandinavia. The vast central plateau of Asia is, owing to difficulty of access and climatic extremes, so isolated from other regions that very little development of any kind, on modern lines, has taken place. High mountain ranges are also barriers to communication, and so tend to separate peoples. Traffic across mountains is limited to the passes, which are often so high as to be snowbound in winter. Such ranges as the Alps, Andes, etc. can only be crossed with great difficulty or by expensive tunnelling.
It sometimes happens that movement of the earth's crust occurs along cracks or faults. Where such movement leaves a block of higher land standing between two areas of lower land, the highland is known as a 'Block Mountain' or horst. The Vosges and Black Forest Mountains are examples of such formations These mountains are usually very steep-sided, and often the summit levels are roughly the same.
When an area of highland remains standing above the general level after rivers and other natural agents have lowered the surface of the surrounding area, the name residual mountain is used. Sometimes such highlands are called 'mountains of denudation'. This term can usually be applied to the mountain ridges associated with 'dissected plateaux'. Included in this class are the mountain ridges of the Highlands of Scotland, the Sierras of Central Spain, and the Mesas and Buttes of the western plateaulands of the United States.
Mountains may be formed by volcanic material piled up around a crater, such mountains are popularly known as volcanoes. Research Mountains
Belemnites are extinct, squid-like molluscs of the Cephalopoda class with a bullet-shaped internal shell. Fossils are found from the Upper Carboniferous period to the Eocene epoch. The fossils are straight, solid, tapering and dart-shaped, and were formerly popularly known as arrow-heads, thunderbolts, finger-stones, etc. Research Belemnite
The crinoidea are the sea lily class of Phylum echinodermata consisting of animals attached during the whole or a portion of their lives to the sea-bottom by means of a calcareous jointed stem, from the top of which radiate feather-like flexible appendages or arms, in the centre of which is the mouth.. The body is cup shaped and attached to the substratum by a stalk. Both the mouth and anus are on the side of the body away from the stalk. The five main arms bifurcate, and on the branches are small side branches. Though comparatively few in number now, they lived in immense numbers in former ages, many carboniferous limestones being almost entirely made up of their calcareous columns and joints. Research Crinoidea
The term ice age was first applied in 1837 by the botanist Karl Schimper (following the proposition of theories by, among others, the Swiss civil engineer Ignace Venetz in 1821 and the Swiss naturalist Louis Agassiz in 1837 in contrast to the held belief that the rocks and sediment left behind were caused by the biblical flood) to refer to a period of glaciation occurring in the Earth' s history, but is particularly applied to that in the Pleistoceneepoch, immediately preceding historic times when an ice sheet spread over northern Europe, leaving its remains as far south as Switzerland. There were several glacial advances separated by interglacial stages during which the ice melted and temperatures were higher than today. There were once thought to have been only three or four glacial advances, but recently it has been discovered that about twenty major incidences have occurred during earth's history. Other ice ages have occurred throughout geological time: there were four in the Precambrian era, one in the Ordovician, and one at the end of the Carboniferous and beginning of the Permian. The occurrence of an ice age is governed by a combination of factors known as the Milankovitch hypothesis: firstly, the Earth's change of attitude in relation to the Sun; and secondly the 92,000-year cycle of eccentricity in the earth's orbit around the Sun, changing it from an elliptical to a near circular orbit, the severest period of an ice age coinciding with the approach to circularity. Research Ice Age
In geology, the Carboniferous was the seventh geological period, 250,000,000 years ago. This era marked the formation of the coal beds. It is the great group of strata which lie between the Old Red Sandstone below and the Permian or Dyas formation above, and is named from the quantities of coal, shale, and other carbonaceous matter contained in them. They include the coal measures, millstone grit, and mountain limestone, the first being uppermost and containing the chief coal-fields that are worked. Iron-ore, limestone, clay, and building-stone are also yielded abundantly by the carboniferous strata which are found in many parts of the world often covering large areas. The thickness of the coal measures in South Wales has been estimated at 10,000 to 13,000 feet. As coal consists essentially of metamorphosed vegetable matter, fossil plants are very numerous in the carboniferous rocks, more than 1500 species of them having been named, a large proportion of which are ferns, tree, lycopods and large horse-tail like plants. The animals include insects, scorpions, amphibians, numerous corals, crinoids, molluscs, cephalopoda, sharks and other fishes. Research Carboniferous
Chert (hornstone) is a mineral very similar to flint, but coarser and less uniform in colour. It is found principally in association with limestones, especially in the carboniferouslimestone of Ireland where beds of it are found several hundred feet thick. It appears to have resulted from the solution and redeposition of the silica of certain kinds of fossils, particularly of sponges, with the pointed spicules of which it is often filled. Radiolarian chert is a streaky, dark-grey, brown or reddish rock which under the microscope is seen to consist of innumerable shells of Radiolaria firmly united together by a siliceous cementing material. Research Chert
Coal-measures are the upper division of the carboniferous system, consisting of beds of sandstone, shale, etc, between which are coal-seams. Research Coal-Measures
Coal is a solid, opaque, inflammable substance, mainly consisting of carbon, found in the earth, largely employed as fuel, and formed from vast masses of vegetable matter deposited through the luxuriant growth of plants in former epochs of the earth's history. In the varieties of coal in common use the combined effects of pressure, heat, and chemical action upon the substance have left few traces of its vegetable origin; but in the sandstones, clays, and shales accompanying the coal, the plants to which it principally owes its origin are presented in a fossil state in great profusion, and frequently with their structure so distinctly retained, although replaced by mineral substances, as to enable the microscopist to determine their botanical affinities with existing species.
The sigillaria and stigmaria, the lepidodendron, the calamite, and tree-ferns are amongst the commoner forms of vegetable life in the rocks of the coal formation. Trees of considerable magnitude have also been brought to light, having a recognizable relation to the modern araucaria. The animal remains found in the coal-measures indicate that some of the rocks have been deposited in fresh water, probably in lakes, whilst others are obviously of estuarine origin, or have been deposited at the mouths of rivers alternately occupied by fresh and salt-water. The great system of strata in which coal is chiefly found is known as the Carboniferous. There are many varieties of coal, varying considerably in their composition, as anthracite, nearly pure carbon, and burning with little flame, much used for furnaces and malt kilns; bituminous (popularly so called) or 'household coal'; and cannel or 'gas-coal,' which burns readily like a candle, and was much used in gas-making. The terms semi-anthracitic, semi-bituminous, caking-coal, splint coal, etc, are also applied according to peculiarities. All varieties agree in containing from. 60 to over 90 per cent of carbon, the other elements being chiefly oxygen and hydrogen, and frequently a small portion of nitrogen.
Lignite or brown coal may contain only 50 per cent of carbon or less. For manufacturing purposes coals are generally considered to consist of two parts, the volatile or bituminous portion, which yields the gas used for lighting, and the substance comparatively fixed, usually known as coke, which is obtained by heating the coal in ovens or other close arrangements, and thus removing the volatile or smoke-yielding matter, while the full heating power of the coal still remains in the coke. Coal was the most valuable of all the minerals which contributed to the former wealth of Great Britain, and it has been mined there for many centuries. The first charter giving liberty to the town of Newcastle-upon-Tyne to dig coal was granted by Henry III in 1239; in Scotland a charter was granted to the abbot and convent of Dunfermline in 1291 for the same purpose. The working of coal gradually but slowly increased, until towards the end of the 18th century, when the development of the steam-engine by James Watt enormously increased the use of coal, and made it the basis of Great Britain's industrial importance. Towards the end of the 20th century political disputes between the miners and the government led to the closure of most of Britain's coal mines, with coal being imported instead. Research Coal
In geology, a formation is any series of rocks referred to a common origin or period, whether they consist of the same or different materials. Geological strata are divided into certain groups of one era of deposition, sometimes of very dissimilar mineralogical character, but inclosing the same fossil species; such as, the Carboniferous, Oolitic, Cretaceous, Silurian, Laurentian, etc. Research Formation
Galena (lead sulphide) or galenite is virtually the only source of lead and an important ore of silver. It is found both in masses and crystallized in cubes, but sometimes in truncated octahedra and has the formulae PbS and a relative hardness of 3. It is a very common metallic mineral, its colour is bluish-grey, like lead, but brighter; its lustre metallic; texture foliated; fragments cubical; soft, but brittle. When found in veins that show a connection to igneous rocks, it is frequently found with silver minerals. Galena is also found in limestones either as veins or as a replacement deposit.
Galena effervesces with nitric and hydrochloric acids. For the most part it contains about 86.6 per cent of lead and 13.4 of sulphur, generally some silver, and also antimony, zinc, iron, and bismuth. Where the proportion of silver is high it is known as argentiferous galena, and worked with a view to the extraction of this metal. Galena occurs principally in the older or primary rocks, being found in England mainly in the Mountain Limestone (base of the Carboniferousformation). In the United States it is very abundant, the deposit of galena in which the mines of Illinois are situated being extensive and important. Research Galena
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Mountains
