Strait of Hormuz

The Strait of Hormuz is a narrow passage of sea water between the Arabian Peninsula and a portion of the southern coast of Iran, mainland Asia. Having an arch shape, it connects the Persian Gulf with the Gulf of Oman, which, in turn, fans out into the Arabian Sea. The strait is approximately 150 km long and is 55.6 km wide at its narrowest point. The shallowest depth in the navigational channel is 71 m. The Iranian port of Bandar Abbas is on the strait. On the western portion of the Strait of Hormuz, there is a relatively large island near the coast of Iran; it is the Qeshm Island. The Musandam Peninsula, which belongs to Oman, and the United Arab Emirates' northeastern coasts, form the southern shores of this sea passage.

About 35% of the world's oil production is shipped through the Strait of Hormuz, and about 17 gas and oil tankers per day move through this sea passage. Therefore, this strait is a strategic energy hub of the world and a geopolitical arena of super powers. All the oil that exits the Persian Gulf through the Strait of Hormuz is produced by Iran, Saudi Arabia, Kuwait, and United Arab Emirates. All this area is surrounded by both Iranian and US military bases. In an event of a war between Iran and the United States, Tehran stated that it could shut off the strait and that it would not let any tanker headed for either the USA or Europe sail through. To protect and be able to fully control this strait, Iran has set up a series of medium-range anti-ship missile launching platforms all along the norther shore of the sea passage.

Map of the Strait of Hormuz that joins the Persian Gulf and the Gulf of Oman.

Map of southern portion of Middle East region showing the Persian Gulf, the Strait of Hormuz, and the Gulf of Oman, and the countries surrounding these bodies of sea water.

Geology of Mount Everest

It took many years to determine the geology of Mount Everest; in other words, to establish its rock composition and geological history. Geologists have agreed to divide the rock structure of the highest peak in the world into three types of geological formations. Each one of them is separated from the other by low angle faults, which are fracture in the continuity of a layer of rock. Meanwhile, the formation and elevation of Mt Everest to the highest point (8,848 m) on the planet surface is, like the rest of the Himalaya, the result of the tectonic collision of the Indian plate against the Eurasian plate, which began about 40 million years ago, during the Tertiary period of the Cenozoic era.

The geology of Mount Everest tells us that this massif is composed of both sedimentary (limestone) and metamorphic rock arranged, as mentioned above, into three types of geological formations, which are kept apart from one another by faults. Thus, from the summit of Mt Everest to its base, these rock structures are the Qomolangma Formation, the North Col Formation, and the Rongbuk Formation. About 70 million years ago, these layers of rock used to be part of the sea bed of the extinct Thesys Ocean, long before the Indian-Australian plate began pushing north against the Eurasian plate.

Qomolangma Formation- It runs from the summit to the top of the yellow band (from 8,848 m to 8,600 m of altitude). It consists of Ordovician limestone, dolomite, and siltstone. The limestone of the summit is composed in turn of finely fragmented remains of trilobites, crinoids, and ostracods, ancient creatures that used to inhabit the ocean floor.

North Col Formation- It makes up the bulk of Mt Everest, with the Yellow Band constituting its upper portion. It lies between the 8,600 m and 7,000 m of altitude. The Yellow Band consists mostly of Cambrian diopside marble, which weathers to a distinctive yellowish brown. The remainder of the North Col Formation is composed of schist, marble, and phyllite, all three being metamorphic rocks.

Rongbuk Formation- It lies right under the North Col Formation, forming the base of Mount Everest. It is made up of sillimanite-K-feldspar grade schist and gneiss intruded by numerous sills and dikes of leucogranite ranging in thickness from 1 cm to 1,500 m (0.4 in to 4,900 ft). Leucogranite is granitic, igneous rock that is part of a belt of Late Oligocene–Miocene intrusive rocks known as the Higher Himalayan leucogranite. They formed as the result of partial melting of Paleoproterozoic to Ordovician high-grade metasedimentary rocks of the Higher Himalayan Sequence during the subduction of the Indian Plate.

South face of Mt Everest. Photo taken in May 1952 by the Swiss expedition.

Volcanic Rock

Volcanic rock (volcanite) is formed as a result of volcanic eruptions. Depending on the type of explosion (a lava flow or explosive eruption), three types of rock are formed: intrusive, extrusive, and volcanogenic-detrital (pyroclastic) rock. They make up ninety percent of the Earth's crust and they have been building up from hundreds of millions of years ago, from the archean eon, the earliest phase of the Earth geological evolution.

Intrusive rock, also known as plutonic, is a volcanic rock formed in the process of injection and solidification of magmatic melt deep in the earth’s crust (intrusion, intrusive body, plutonic intrusion). Thus, this type of rock cooled off and solidified deep under the surface of the Earth. Granite, diorite, and granodiorite are the three types of intrusive rock and they are found in the shape of laccoliths and lopoliths, as well as batholiths, stocks, and dikes, all of which are magma formation by intruding deep under the surface of the planet. Intrusions are classified according to the depths at which the magmatic intrusion occurred as deep-seated intrusions (abyssal) and shallow-depth intrusions (hypabyssal). In this context the conditions of cooling of the magma and its effect on surrounding rock differ sharply. At shallow depths the cooling is rapid and fine crystalline or porphyritic rock is formed, and contact metamorphosis affects a small area of the country rock. At great depths medium-grain and large-grain rock and major changes in the surrounding rock are characteristic.

Extrusive rock (or effusive), on the other hand, is a magmatic rock formed with the cooling of lava on the earth’s surface or within the crust under near-surface conditions in contact with the atmosphere. Basalt is the hardest and the oldest type of extrusive rock. A significant proportion of the effusive rocks was formed during the eruption of underwater volcanoes. Typical characteristics of effusive rocks, associated with the rapid cooling of lava, are the presence of volcanic glass in their composition and, often, a unique porphyritic texture. The composition of effusive rocks varies widely. Basalts, andesites, and rocks intermediate between basalts and andesites are most common. Dacites and liparites are less common. Alkaline effusive rocks, such as phonolites and leucites, and ultrabasic effusive rocks, such as comateite, are even rarer. Effusive rocks were found on the moon. Effusive rocks are contrasted to intrusive rocks.

The volcanogenic-detrital (or pyroclastic) rock is divided into friable (volcanic ash, sand, bombs, and so on), compacted, and cemented rock (tuff, tuff breccia, and others). In addition, there are intermediate types of volcanic rocks: tuff lavas, which occur as a result of eruptions of gas-rich foaming lava flows, and ignimbrites, which occur as a result of violent eruptions when pieces of lava are carried into the air and fall on to the surface, forming masses of melted matter that occasionally occupy wide areas measuring hundreds and thousands of square kilometers.

Diadorite is a plutonic (intrusive) rock. It looks like granite and it is also extremely hard.

Mount Kilimanjaro

Mount Kilimanjaro is a massive elevation of volcanic origin located in East Africa, in Tanzania. It reaches an altitude of 5,895 m (19,340 feet), which is the highest point on the continent. This volcanic massif was formed from the merger of three dormant volcanoes: Kibo (5,895 m), Mawensi (5,355 m), and Shira (4,006 m). Kibo’s crater, up to 2.5 km wide and up to 180 m deep, has an inner cone with a relative height of about 580 m and a crater more than 800 m wide. It was climbed for the first time in 1889, and it is a great tourist attraction.

Lying about 160 km (100 miles) east of the East African Rift System, Mount Kilimanjaro is a dormant stratovolcano that consists of three cones; Kibo, Mawensi, and Shira. The volcanic activity of the Shira cone began 2.5 million years ago, while Kibo and Mawensi started to erupt one million years ago as these two cones are separated by the Saddle Plateau at an altitude of 4,400 m (14,400 feet) . Geologically, it is composed mainly of trachybasalts and phonolites, which are volcanic extrusive rocks composed of feldspars.

On the humid southern and southwestern slopes, at an elevation of about 3,100 m, annual precipitation ranges from 1,000 to 3,000 mm. From the foothills to 1,000 m, the slopes are covered with savannas, and coffee and banana plantations, growing on the site of cut forests, are found to 1,800 m. Tropical rain forests with epiphytes and ferns extend to 3,100 m, tropical alpine vegetation (paramos) is found to 4,200 m of altitude, and xerophytic pulvinate grasses grow to 4,800 m. Above 4,800 m are lava fields, and on the crests, glacial relief forms predominate, with glaciers descending as far as 4,300 m on the western slopes.

Mount Kilimanjaro; Kibo cone (5,895 m).

Cascade Range

The Cascade Range is a mountain range located in the northwestern portion of the United States and southwestern part of Canada. It is 1,100 km (700 miles) long and extends from south to north through the State of Oregon, Washington, and British Columbia in Canada. With 4,392 m (1,411 ft) of altitude, Mount Rainier is the highest peak of this mountain system, while Mount St. Helens and Mount Hood are active volcanoes. In 1980, Mount St. Helens erupted with extreme violence and it was recorded on film. The Cascade Range gets its name from the abundance of terrace-like waterfalls (cascades) on the Columbia, Fraser, Klamath, and other rivers that cut through the range.

Geologically, the range is composed of Mesozoic crystalline rocks, which was later covered by huge layers of Paleogene and Neocene lavas. However, the Cascade Mountains belong to the Tertiary orogeny of the Cenozoic era, as it was formed and elevated by the collision and subduction of Juan de Fuca tectonic plate against the North American plate, sliding beneath it. Above this strongly dissected volcanic plateau, which is from 1,800 to 2,500 m high, rise isolated cones of volcanoes, such as Mount Baker, Mount Rainier, Mount St. Helens, Mount Hood, and Lassen Peak, with altitudes of 3,000 to 4,000 m and more.

Although most of the volcanoes are extinct, some of them are still active, such as Mount Rainier, Lassen Peak, and Mount St. Helens, which showed their greatest volcanic activity in the late 19th and 20th centuries. Signs of volcanic activities can be seen in mountain slopes, which abound in fumaroles and hot springs. The volcanic peaks are covered with vast snow fields and glaciers. Dark coniferous forests grow on the humid western slopes of the range and pine trees on the dry eastern slopes; above 2,800–3,000 m, the forests give way to subalpine and alpine meadows. There are copper and gold deposits in the mountains. Crater Lake, Mount Rainier, and Lassen Volcanic national parks are located in the Cascade Range.

The Cascade Range extends from Oregon to Canada.

Cenozoic Era

The Cenozoic era is the geological time span in which we are living now. It began 66 million years ago right after the Mesozoic. This present time era is divided into two periods, the Tertiary and the Quaternary (Anthropogenic). The Tertiary is characterized by the formation of the newest and largest mountain ranges on the planet, which have the highest peaks, such as Himalaya, Andes, and the Rocky Mountain Range. The Quaternary, on the other hand, is marked by the four glaciation ages and the emergence of big carnivores and human beings. This era also contains the top strata (layers) of the Earth's crust.

If the Cenozoic era is divided into two well-defined periods, each one of these periods consists of epochs. Thus, the Tertiary period is further subdivided into the Paleocene, Eocene, Oligocene, Miocene, and Pliocene. It is very important to point out that during the Miocene the Earth's temperature began to drop as large tracts of forests and jungles started to disappear, giving way to the appearance of the plains, savannas, and steppes, with massive proliferation of graminae (grass) and ruminant herbivores, such as bovines (cattle), ovines (sheep), caprines, and deer. Inordinate numbers of grass grazers triggered the proliferation of big cats and other carnivores, and also human beings; the hunters. The appearance of Homo sapiens would take place during the Quaternary, which geologists divided into two epochs: the Pleistocene and the Holocene (present time); during the Pleistocene, the first humans emerged.

General Characteristics

During the Cenozoic era the present distribution of continents and oceans occurred. The very beginning of the era saw the completion of the breakup of the formerly unified southern continental mass, Gondwana, into the separate continental blocks of South America, Africa, the Indian subcontinent, Australia, and Antarctica, divided by the newly formed basins of the Indian Ocean and the southern part of the Atlantic Ocean —a process that had been under way since the Mesozoic. By the middle of the Cenozoic, Eurasia and Africa formed the continental mass of the Old World, joined by the mountain structures of the Mediterranean geosynclinal belt. The collision of tectonic plates brought about the orogenesis (formation of mountains) of most of the highest mountain ranges on Earth today: the Alps, Himalaya, Andes, Rocky, Cascade Range, etc. During the Quaternary, the large plains rich top soil continue to build up, with grass being the most abundant plant on Earth.

At the beginning of the Cenozoic, the large reptiles, which had predominated during the Mesozoic, became extinct and were replaced by mammals that, with birds, constituted the nucleus of the terrestrial vertebrates of the Cenozoic era. On most continents the higher placental mammals became dominant, and only in Australia (which became isolated before these mammals appeared on a large scale) did unique marsupials and, to some extent, monotremes develop. During the early Paleogene, mammals were represented almost exclusively by small primitive forms. By the middle Paleogene almost all the orders existing today had appeared, as well as several groups that subsequently became extinct. A great variety of mammals evolved and thrived.

Formation of Mountains

The formation of mountains is called orogenesis in geology. This long process of mountain building is caused by the horizontal collision of tectonic plates. In other words, when two tectonic plates collide and push against one another, with one edge sliding and crashing beneath the other's; this is called subduction, which is the result of two tectonic plates convergence. There is crumpling of layers of rocks into folds as they rise up, gaining altitude. As a result, large masses of molten rocks and geological materials are uplifted in vertical tectonic movements, whose rate exceeds that of the exogenous process of destruction and removal (erosion) of rock or the process of buildup of sediments (accumulation), which lead to the leveling of the earth’s surface. Orogenesis, or orogeny, is characteristic of active regions of the earth.

When the term “orogeny” was introduced, it had been established that the crumpling of layers of rock into folds led directly to the formation of mountains. One hallmark of orogeny is the formation of orogenic belts, which are elongated areas of deformation that borders continental cratons. Young orogenic belts, in which subduction is still taking place, are characterized by frequent volcanic activity and earthquakes, such as relatively new mountain ranges from the Tertiary period, like the Himalayas, Andes or the Rocky Mountain Range. Older orogenic belts, on the other hand, are typically deeply eroded to expose displaced and deformed strata. These are often highly metamorphosed and intrusive igneous rocks, which are called basoliths (granite and quartz monzonite).

Orogenesis is a geological term introduced by the American geologist G. Gilbert in 1890 to designate mountain building and intense deformation by folding and faulting. Gilbert singled out orogenic movements of the earth’s crust and contrasted them to epeirogenic movements, that is, slow upward and downward movements. The concept of orogeny was further developed by the French geologist G.-E. Haug, who, in 1907, proposed that orogeny be distinguished only within geosynclinal regions. Subsequently, in 1919, the German geologist H. Stille hypothesized that the chief result of orogeny was not the formation of mountains but rather the formation of folds.

Appalachian Mountains

The Appalachian Mountains constitute the oldest mountain system in North America. Lying in the Northeast of the United States, they form a long belt of ranges and ridges, valleys, plateaus and tableland. They extends for 2,600 km (1,616 miles) in a southwest-northeast direction, from 33° north latitude to 49° N lat. The width of this orographic system varies from 300 km (186 miles) to 500 km (311 miles), The main ranges of the Appalachians are the Blue Ridge Mountains, White Mountains, Adirondacks, and Green Mountains. The Appalachian Plateau should also be noted. Their altitude ranges from 1,300 to 1,600 m, with the highest peak being Mount Mitchell, which is 2,037 m (6,683 feet) high.

The rivers of the Appalachians run through deep valleys. The flow is abundant all year round, providing considerable reserves for hydro-power AC generation. The largest rivers are the Connecticut, Hudson, Susquehanna, and Tennessee. They overflow their banks frequently because of melting snow in the spring and heavy rainfall in the summer. The major rivers of the northern Appalachians are navigable. As they fall from the eastern edge of the Piedmont, most of the rivers form rapids and waterfalls (the so-called fall line), which are used in part for power production.

Climate

The weather of the Appalachian Mountains is modified by the influence of the Atlantic Ocean and especially of the warm ocean current of Gulf of Mexico (or America). It is temperate in the north and subtropical in the south. The average temperature in January ranges from - 12°C in the north to 8°C in the south; in July the average ranges from 18°C to 26°C. Annual precipitation is from 1,000 to 1,300 mm. In the winter there are heavy frosts in the upper zone of the mountains, and much snow falls. The valleys are drier and warmer. The summers are humid and cloudy; rainfall is abundant, especially on the western slopes. The clearest and sunniest weather comes at the end of summer and beginning of autumn.

Geological History

The Appalachians were uplifted on the site of a geosynclinal system which developed actively in the Paleozoic era on a late Precambrian folded foundation. Millions of years later, the mountains were leveled during the Jurassic Paleocene period. Mountains reappeared again in the Neocene-Anthropogenic period, when the territory of the modern Appalachians underwent a domed uplift, which resulted in the vigorous breakup of the surface and the formation of the modern terrain. The ranges consist of folded rocks and boulders and are divided by intermontane erosional valleys and basins.

The northern Appalachians border on the Canadian Shield in the northwest, along a huge fault (the Logan line). They lack frontal sag and consist of a narrow belt of lower Paleozoic sedimentary deposits in the northwest and a wider belt of igneous, intrusional magmatites and metamor-phic rock in the southeast. The main tectonic periods for the northern Appalachians were the Taconic (at the end of the Ordovician) and the Acadian (at the end of the Devonian). During the Carboniferous-Permian period intermontane sag developed in the interior, filled mainly with continental deposits, first coal-bearing and then red in color.

During the Anthropogenic period, the northern partion of the Appalachians underwent glaciation, while the southern part remained in a temperate (mild) and humid climate. As a result, forests of broad-leaved and evergreen trees were able to survive there and subsequently to spread over a large part of the Appalachians. By structure and development the Appalachians are divided into the northern and southern regions (with the borderline approximately at the latitude of New York City).

Above, a map of North America showing the Appalachian Mountains.

Ural River

The Ural river is a large stream of fresh water that flows into the Caspian Sea. It is 2,428 km (1,508 miles) in length and it drains an area of 231,000 Km2. It rises in the Uraltau Range of the Southern Ural Mountains, near Mt. Kruglaya, Russia. It first flows in a westward direction, then it turns left at the city of Uralsk, running southward all the way into the Caspian Sea near the city of Gurev.

In its upper course, the Ural is a mountain river. Then it flows through marshy land, after which its valley alternately narrows and broadens to as much as 5 km. Below Verkhneuralsk, it becomes a plain river. At Magnitogorsk and lower, the river is bounded by rocky banks. It was formerly known as the Iaik river before 1775.

The largest tributaries of the Ural are the Sakmara, Irtek, and Chagan on the right, and the Or, Ilek, and Utva on the left. The Olenti, Kaldygaity, and Uil rivers disappear through seepage loss in the Caspian Lowland without reaching the Ural. The Ural freezes over in early November in the upper course, and in late November in the middle and lower courses. The ice breaks up in late March in the lower course and in early April in the upper course. The period of ice drift is short, and ice jams are common. The river is navigable from Uralsk to Gurev.

The Ural river is fed primarily by melting snow. Spring high water takes place from late March to early April in the lower course, and approximately from the middle of the second week of April to June in its upper course. There is minor flooding in the upper course in the summer and fall, and a stable low water level for the remainder of the year. During high water the river overflows its banks in the middle course and exceeds 10 km in width, broadening in the delta to tens of kilometers. The highest water levels occur in late April in the upper course and in early May in the lower course.

Fauna

Ural river fish of commercial importance include sturgeons of the genus Acispenser, especially stellate sturgeon (A stellatus), and also pike perch, herring, European bream, carp, and European catfish. The cities of Verkhneural’sk, Magnitogorsk, Orsk, Novotroitsk, Orenburg, Ural’sk and Gur’ev are situated on the river. The northern mole and the marbled polecat, as well as sand lizards, turtles, and water snakes are also found on the banks of the river.

The Ural river is marked in dark blue. You can also see the Volga, which also flows into the Caspian Sea.

Ural Mountains

The Ural Mountains are the main orographic system of Russia. Running from north to south, they form the natural boundary between Europe and Asia. This mountain range is 2,365 km (1,470 miles) long and it extends from the Arctic to Kazakhstan, east of the Caspian Sea. The highest peak is Mt Narodnaya, which is 1,895 m (6,216 feet) high. The Urals harbor the richest mineral deposits on Earth as it varies in width from 40 km (24.8 miles) to 150 km (93 miles). Meanwhile, the rivers that originate in the Urals drain either into the Arctic Ocean or into the Caspian Sea. The Pechora and Usa on the western slope and the Tobol, Iset, Tura, Lozva, and Severnaia Sosva rivers (all part of the Ob system) on the eastern slope flow into the Arctic, while the Kama River and the Ural River drain into the Caspian Sea.

The Ural Mountains are divided into the Polar, Subpolar, Northern-Central, and Southern Urals. The Polar Urals have average elevations of 1,000 and 1,200 m, rising to 1,499 m on Mount Paier, with ridges having rounded summits. The Subpolar Urals have the highest peaks, Mount Narodnaya (1,895 m) and Mount Karpinskii (1,878 m), and attain a maximum of 150 km. Many of their ranges, among them the Issledovatel’skii and Sablia, have serrated ridges and are deeply and densely dissected by river valleys. Traces of Pleistocene mountain and valley glaciation in the Polar and Subpolar Urals include cirques, U-shaped valleys, and moraines. Modern glaciation is also extensive; the largest of the 143 glaciers that cover the Polar and Subpolar Urals are the IGAN, MGU, and Dolgushin glaciers. Intergelisols are common.

Stretching from north to south, the Northern-Central Urals consist of a series of parallel ranges rising to 1,000–1,200 m and longitudinal depressions. They typically have flat summits, although the upper parts of the higher mountains, notably Tel’posiz (1,617 m) and Konzhakovskii Kamen’ (1,569 m), have a more rugged topography. The greatly worn down Central Urals are the lowest mountains in the system, rising to 994 m on Mount Srednii Baseg. The topography of the Southern Urals is more complex. The numerous ranges of different elevations, trending southwest or north-south, are dissected by deep longitudinal and transverse depressions and valleys. The highest peak is Mount Iamantau (1,640 m).

Karst topography (area of limestone) is extensively developed on the western slope of the Urals and in the Ural Region, particularly in the basin of the Sylva River, a tributary of the Chusovaia. There are many caves (Div’ia, Kungur, Kapova), basins, sinks, and underground streams. The eastern slope has fewer karst formations. Rocky outliers such as the Sem’ Brat’ev, Chertovo Gorodishche, and Kamennye Palatki rise above its flattened or gently rolling surface. Wide foothills, reduced to peneplain, adjoin the Central and Southern Urals on the east, broadening the Southern Urals to 250 km.

Minerals

The Ural region holds many useful and valuable minerals used by the industry. Forty-eight of the 55 most important minerals processed and used in Russia are found in the Urals. The eastern Urals are noted for their deposits of copper pyrite (Gai, Sibai, and Degtiarsk deposits and the Kirovgrad and Krasnoural’sk groups of deposits), skarn-magnetite (deposits of Mount Vysokaia, Mount Blagodat’, and Mount Magnitnaia), titanomagnetite (Kachkanar and Pervoural’sk), nickel ironstone (Orsk-Khalilove group of deposits), and chromite ores (deposits of the Kempirsai massif), mostly confined to the greenstone belt.

The eastern slope also has coal seams (Cheliabinsk coal basin) and placer and native deposits of gold (Kochkar’, Berezovo) and platinum (Isovka). The Severoural’sk Bauxite Region and the vast Bazhenov asbestos deposits are on the eastern slope. On the western slope of the Urals and in the Ural Region there are deposits of hard coal (Pechora and Kizel coal basins), petroleum (Volga-Ural Oil-Gas Region, Orenburg gas condensate deposit), and potassium salts (upper Kama basin). The Urals are especially famous for their precious, semiprecious, and ornamental stones, including emeralds, amethysts, aquamarine, jasper, rhodonite, and malachite. The best jeweler’s diamonds in Russia come from the Urals.

Geological Structure

The Ural Mountains are a late Paleozoic (Hercynian) folded region lying within the Ural-Mongolian folded geosynclinal belt. Deformed and frequently metamorphosed rocks, chiefly Paleozoic, crop out on the surface in the Urals. The region’s sedimentary and volcanic strata are highly folded and broken by fractures, but in general they form north-south bands, which account for the linear and zonal structure of the Urals.

Six geological zones may be distinguished from west to east: (1) the Cis-Ural Foredeep, with a comparatively gentle bedding of sedimentary layers on the west and a more complex bedding on the east; (2) the Western Slope Zone, whose Lower and Middle Paleozoic sedimentary layers are intensively folded and dislocated by thrusts; (3) the Central Ural Uplift, where the more ancient crystalline rocks of the margin of the East European Platform crop out in places among Paleozoic and Upper Precambrian sedimentary strata; (4) the “greenstone belt,” a system of troughs and synclinoria on the eastern slope (of which the largest are the Magnitogorsk and Tagil’ synclinoria), filled chiefly with Middle Paleozoic volcanic strata and marine (often deep-sea) sediments intruded by plutonic igneous rocks (gabbroids, granitoids, and sometimes alkaline intrusives); (5) the Ural-Tobol’ Anticlinorium, with outcrops of more ancient metamorphic rocks and extensively developed granitoids; and (6) the Eastern Ural Synclinorium, in many ways similar to the Tagil’-Magnitogorsk synclinorium.

Using geophysical data, Soviet geologists had established that the first three geological zones rest on an ancient Precambrian basement composed chiefly of metamorphic and magmatic rocks and formed in the course of several epochs of folding. The most ancient rock, believed to be Archean, crops out at the Taratash protrusion on the western slope of the Southern Urals. Pre-Ordovician rocks are unknown in the basement of the synclinoria of the eastern slope of the Urals. It is thought that the thick plates of ultrabasites and gabbroids that crop out in places in the Platinonosnyi and analogous belts serve as the basement of the Paleozoic volcanic strata of the synclinoria. These plates may possibly be broken-off remnants of the ancient sea floor of the Ural geosyncline. Some ancient outcrops in the Ural-Tobol’ Anticlinorium in the east are perhaps Precambrian.

The Paleozoic beds of the western slope of the Urals are composed of limestones, dolomites, and sandstones that were formed for the most part in shallow seas. To the east lies a discontinuous strip of deep-sea continental slope sediments. Still further to the east, on the eastern slope of the Urals, the Paleozoic (Ordovician and Silurian) cross-section begins with altered basaltic volcanites and jaspers that are comparable to the rocks of the present-day ocean floor. Thick spilite-natroliparite strata, also altered and containing deposits of copper pyrite ore, occur in places higher up in the cross section.