Sketch Of The Geology Of Scandinavia
( Originally Published 1881 )
Scandinavian Geology.—Former Finland Gulf and Arctic Climate.—Primary Rocks. —Azoic Ores.—Silurian formation, and Characteristic fossils.—Former greater extent.—Rarity of Devonian and absence of Carboniferous strata.—Eruptive Rocks.—No Mesozoic in Sweden except the Lias and Chalk.—Absence of the Tertiary formations.—Extent and Changes of the Past—Post-tertiary, smalLGlacial Epoch and its phenomena.—Sand, Marl, and Clay deposits.
GEOLOGY, the science which has disclosed to us, page by page, the history of past creations, and which is constantly revealing new facts, has demonstrated beyond controversy the immense lapse of time that has been required to work out the physical changes on the earth, and to permit the development and extinction of the great number of vegetable and animal forms which are found in large quantities over wide areas of its surface.
The peninsula of Scandinavia presents very interesting geological and physical features. A great part of the country was uplifted above the ocean at a very remote period, and there is no other region which exhibits at the surface, comparatively, more extensive areas of the primary rocks constituting a large portion of the oldest crust of the globe.
According to Professor Erdmann, a most distinguished Swedish geologist, a gulf formerly passed from the Arctic Ocean, at Archangel, across Finland—which was then at the bottom of the sea—down to Gotland, or even farther. This he deter-mines from the presence of fossil shells such as Yoldia pygmcea) in the boulder clay of the coast of the Baltic, and central parts of Sweden, now found only in the latitude of Spitzbergen. The shell banks on the coast also indicate a former more severe climate—the highest ones bearing remains of arctic species; the middle ones, of more temperate life; and the lowest, of species now existing on the coast. Professor Lovén also found arctic marine crustaceans living at the bottom of the deep lakes Wener and Wetter, proving that these were once connected with the gulf above alluded to.
The fundamental rocks are gneiss, mica-schist, hornblende, chloritic slates, and quartz ; gneiss is the most prevalent, occur-ring as gray or red gneiss, hornblende gneiss, etc. Among the eruptives granite is the most common in Sweden, occurring with syenite everywhere. Pegmatite, or graphic granite, generally occurs in veins. Mica slate and clay slate occupy much less extent than the granite and gneiss ; the former is found in the central parts, especially in Jemtland, near the Storsjö Lake, and farther south; the clay slates are, however, more rare. In some districts of Norway, between the coast and the mountains, the azoic mica-schists include veins of eruptive masses, especially granite and serpentine, and sometimes green-stone, even the more recent rocks are thus penetrated ; occasionally the old granite mountains are diversified by slates.
The Kjôlen range comprises a chain following the boundary-line from the Skjker mountains in the north to Faxefjeld in the south ; in the north its rocks are imperfectly known, but the central part has sparamite in the middle, Trondhjem slates on both sides, and granite and gabbro masses both in the central axis and in side lines; in the south the range disappears in table-land, which, with Faxefjeld, runs into Sweden.
In the extreme northern part of Norway the primary rocks are less prevalent, being mostly covered with more recent rocks, consisting of slates, sand, and limestones of different kinds. In Finmarken, of eruptives are found gabbro, green-stone, and granite, though not so extensively as in other parts of Norway. Central Norway is chiefly of sparamite formation, with overlying clay slates and quartz in broad belts.
The Dovre range forms one part of the coast, with several spurs extending from Romsdal fjord, as immense granite parallel walls running towards the sea; its middle portion is penetrated by sparamite, with Trondhjem slates and mica-schist on both sides, and gabbro and granite at the base.
Hornstone (flint) occurs in several provinces—sometimes, evidently, transformed schists, at other times amorphous; the same is true of porphyry; diorite and hyperite generally occur in stocks, or in veins in the gneiss ; diabase is common, and forms the summits of some of the mountains.
In Norway there is much hornblende and quartz slate, gray gneiss and green slate-either one forming the principal rock or the gneiss, overlaid by the slates. In many of the great granite ranges are rich quarries of felspar.
All the ores of Sweden occur in the oldest azoic formations —copper, nickel, iron, silver, cobalt, phosphate of lime, and gold in small quantity; in some districts the iron is titaniferous, and occasionally entirely above the surface.
The Silurian strata are most developed in central Sweden. The order of succession of the strata is gneiss, or other fundamental rocks, sandstone, aluminous shale, with swinestone, red or gray limestone, and clay slate; the uppermost stratum is eruptive trap; in some districts the limestone and clay slates are wanting, and the trap rests upon the alum shale, the strata being then horizontal.
The lower Silurian strata generally do not vary much from horizontal; but in some places—for example, on the side of Lake Wetter—they have a very sharp inclination, on account of the upheaval of the underlying rock; they consist of conglomerates, sandstones, and grayish slates.
The characteristic fossils are, among the brachiopods, Strophomena depressa; among the cephalopods, Orthoceras; among the articulates, the trilobites, which are the most common of the fossils.
The older formations often form table-lands, with a gentle slope; they are in places 2000 feet thick, but towards the south grow thinner, and are finally completely covered by more recent strata. The Dyktyonema slate and limestone, with accompanying quartz, occur in the high mountain regions in two thick series-the lower with mica-schist, sometimes with alum slate, the upper with different colored and often quartzy slate; clay slates are found with a thickness of 1000 feet, and over these limestone, sometimes in distinct beds, covered in many places by calcareous sandstone—in one place a lime breccia, in another a hard sandstone, containing several species of trilobites. he upper Silurian rocks may be named after their fossil contents, coral and sea-plants, etc. Silurian strata, with Diktyonema, are seen at Hulberget, 4000 feet above the sea; and at Tunsâs, near Valders, with Olenus, 2500 feet high.
The Silurian formation was once far more extended than at present, as is shown by the prevalence of stratified marls, consisting chiefly of carbonate of lime, derived from previous Silurian limestones : fragments and blocks of the latter are scattered over some districts. Over the most recent Silurian limestone is more than 1000 feet of red and gray clay slates, containing, as far as known, no traces of life, probably corresponding to the Devonian period.
The Devonian formations are found only on three islands of Lake Malar, as shown by characteristic fossils.
The Carboniferous formations are entirely wanting.
According to Kjerulf, there are eruptive masses more re-cent than the crystalline granites, syenite and porphyries ; near Christiania fjord, are large eruptions of serpentine granite, syenite, and greenstone in the high mountains, and near the boundary-line.
In some districts, recesses and dikes in the gneiss are filled with couglomerates and sandstones. The masses of eruptive granite form high and ragged mountains, often with, grandly precipitous walls, the naked barrenness of which contrasts singularly with the fertile slate districts. In the great granite areas are a few marble strata surrounded by Labradorite ; iron and copper pyrites, with much sulphur, are not uncommon; the strata of Silurian marble and other limestones may be 900 feet thick, occupying the uppermost part of the deposit, containing numerous fossils, as favosites, encrinites, macra, etc.
Of the Mesozoic formations, the Triassic, Jurassic, and Weald-en are not found in Sweden. The Lias is found in the most southern part, in the neighborhood of Hoganas ; the strata are quite thick, consisting of sandstone, clay slate, and plastic clay, with intervening strata of coal, the thickest of which is only four feet. This formation is poor in fossils, but a typical species, Avicula incequivalvis, has been found.
The chalk occurs only in detached places in south-eastern and southern Sweden, the older strata consisting partly of whitish-gray limestone, containing numerous fragments of mussel-shells. In other places it is a sandy lime, with grains of green sand. The more recent strata consist of limestone, with chalk and flint nodules. Among the fossils found is a brachiopod (Crania ignabergensis).
No traces of Tertiary formations have been found in Sweden; the Post-tertiary period, however, there is of special interest to the geologist. The surface changes of the earth, which, from the end of the Silurian epoch, have occurred in the Old and the New World, have, as a general rule, not affected Sweden ; the Devonian has left mere traces of its existence; the Mesozoic, in other countries so extensive and important, is found only in the southern part. -
The Post-tertiary formations of Sweden and Norway show that, notwithstanding the great changes of surface experienced by the more southern portions of the European continent, the Scandinavian peninsula, up to comparatively recent times, has preserved nearly its ancient relative level above the sea, with the exception of the lias and the chalk in its southern part. As on the American continent, at the beginning of the Post - tertiary epoch, the northern parts of Europe were elevated above the ocean, a diminution of temperature accompanying the increase of the land, which covered the whole country with ice—constituting the " Glacial period." Then came a subsidence beneath the sea, allowing the accumulation of marine, lake, and river formations, corresponding to the " Champlain epoch" of American geologists. An elevation of the land then took place—the so-called " Terrace epoch"—when the surface assumed the height and characteristics which we now see. The " Post-tertiary epoch," both in Europe and North America, was a period of high - latitude oscillations, as above stated—upward, downward, and again upward, and comparatively stationary.
The fields of loose soil, which occupy the plains as well as the valleys, river-basins, and many plateaus, are of two kinds: those which mark the sea-level, generally 500 or 600 feet above the present one, with clay and sandstone, are rich in marine shells and fossils of arctic seas, and show traces of old shore lines ;. the higher ones, with gravel and sand, but with-out large clay fields, contain no marine fossils.
It has been seen that the geological formations between the Carboniferous and the Post-tertiary are not found in Norway and Sweden, with the exception of the Lias and Chalk formations, which are found in Skâne and Blekinge, and of a few Mesozoic strata in one spot, in the extreme north of the province of Finmarken ; that the Post-tertiary rests directly on the Palozoic. The azoic rocks are more extended and thicker than in any other country of equal area. During the Glacial period the whole of Scandinavia was buried under the ice. The immense glaciers have left their marks in the fur-rowed land, striated rocks, deep valleys, extensive fjords, huge moraines, etc. ; from the sea- level to almost the tops of the highest mountains, the rocks are grooved by strie or scratches, their surfaces perfectly polished ; the angular mountains have been rounded into roches moutonnées, and boulders are left even at the height of 5000 feet above the sea. Moraines —the accumulations of loose matter left by the melting and retiring glaciers, composed of huge stones, angular rocks, gravel, sand, and clay—are met with everywhere, at various elevations, and high up on the mountain-sides.
When the inland ice melted, many valleys were left for a long time ice-filled ; the glaciers retreated, however, higher and higher; and,where they for a long period. remained stationary, their moraines formed a dam for the water, which increased in depth, allowing the quiet deposition of the clay beds, now found here and there in the valleys.
In different districts the materials of the soil vary accordng to the geological constitution of the mountains over which the glaciers ground their way ; clay or lime predominating, as the case may be.
The period following the Glacial was that of the Roll-stone, or Sand-ridges, the beginning of the Champlain epoch of the American geologists, followed by the deposition of the diluvial clays. Such ridges are very common in Sweden; the most remarkable are at Badelundsas, near Westerns, and Brunkeberg, in Stockholm; the celebrated mounds at old Upsala are situated at the end of such a ridge. They are formed of several strata, the lowest consisting of gravel with rounded stones, and above these sand, with interjacent clays; their. height above the surrounding country is 100 to 150 feet, and their direction generally north and south. Other deposits during this period are sand as a coast formation, or in shallow water; stratified marl, and clay without lime or magnesia, deposited in a deep, calm arctic sea ; and black clay, with variations of blue and gray, belonging to a later period; when the sea began to assume its present limits. The sand is found directly on top of the glacial gravel, from which it differs by its stratification, and its apparently washed condition ; the stratified clays, and in some places the stratified marls, constitute the lowest stratum : the fossil mussel (Yoldia glacialis) shows that the sea from which the clay was deposited was an arctic one.
The clay on top of the marl is black clay, which merges into the common clay; in this occur fossil shells, the same as those living in the Baltic, such as Tellina baltica, (Cardium edule, and Mytilus edulis. Enclosed in these clays and sands are found large stones, probably carried by icebergs and dropped into the strata under formation; the same is the case with so-called erratic blocks found in many places in Scandinavia.
In the upper clays and sand are found, especially in the western part of the country, beds of shells of species now living in the North Sea, or still farther north. Such a bed is seen at Kapellbacken, near Uddevalla, and contains Pecten islandicus and others.