Magnesian limestone

“ Bees Head by bituminous clay, over this is a limestone containing magnesia and iron, and above this is a red sandstone, connected with which is clay, marl, and gypsum. This it will be perceived is almost an exact account of the succession of the red ground strata in this quarter. In Derbyshire we are informed that the magnesian limestone lies in an unconformable and horizontal position over the inclined strata, after the manner of its occurrence in this quarter, it therefore plainly belongs to the same formation, the red ground. ”

“ The Magnesian Limestone deposits succeed the carboniferous, and sometimes pass into them by insensible gradations. In the south of England they are represented by conglomerates, and partly composed of the solid and more or less rounded fragments of the older strata. They afford a proof of what geologists have often occasion to remark of the long periods of time during which the ancient works of nature were perfected; for the older rocks were solid as they are now, and their organic remains petrified at the time these conglomerates were forming. ”

“ A hollow space formed like a basin or trough is filled with the limestone. [3] The length of this from east to west is about a mile; the breadth from north to south four hundred yards, the depth seventy feet. The beds pass over the ninety-fathom-dyke; which has occasioned in them no confusion or dislocation; so that there can be little hazard in stating that the beds of the magnesian limestone belong to a more recent formation than those of the Coal-field. The limestone has been quarried across its whole breadth, and a numerous set of thin strata are thus exhibited to view. ”

“ It is of this stone (selected on account of the durability it has shown in York Minster and other old buildings) that the Houses of Parliament are built. Now, although very few fossils are found in this rock, yet I believe that most geologists would agree that it was originally formed, like limestones generally, by the growth of corals, shells, etc., which separated the carbonate of lime from the sea-water they inhabited; its subsequent conversion into magnesian limestone having been probably effected by the infiltration of water in which magnesia was dissolved. ”

“ Peculiar in their mineral composition, rocky structure, and the nature and distribution of their imbedded organic remains, the constituent members of the red sandstone and magnesian limestone sometimes offer many points of inquiry to the inductive geologist, and much that seizes on the imagination of those who venture freely into the unsafe regions of speculation. ”

“ Fig. 347. Acrolepis Sedgwickii, Ag. Marl-slate.
The inferior sandstones (No. 6. Tab. p. 301.) , which lie beneath the marl-slate, consist of sandstone and sand, separating the magnesian limestone from the coal, in Yorkshire and Durham. In some instances, red marl and gypsum have been found associated with these beds. They have been classed with the magnesian limestone by Professor Sedgwick, as being nearly co-extensive with it in geographical range, though their relations are very obscure. ”

“ Permian magnesian limestone succeeds the Coal Measures on the east, it reaches from the Tees to South Shields in a broad tract and occupies the coast between that town and Hartlepool. Remarkable concretionary forms are found in the Fulwell Quarries simulating honeycomb and coral structures. The 707 stone is quarried at Marsden for the manufacture of Epsom salts; it is also used for lime-making and building. ”

“ Brucite is generally associated with other magnesian minerals, such as magnesite and dolomite, and is commonly found in serpentine, or sometimes as small scales in phyllites and crystalline schists; it has also been observed in metamorphosed magnesian limestone, such as the rock known as predazzite from Predazzo in Tirol. The best crystals and foliated masses are from Texas in Pennsylvania, U.S.A., and from Swinaness in Unst, one of the Shetland Isles. ”

“ But whatever number of groups may be present, they never happen out of their regular order of succession; that is, clay-slate never occurs above coal, nor coal above chalk. Thus in London, tertiary strata occupy the surface; in Durham, magnesian limestone; in Fife, the coal measures; and in Perthshire, the old red sandstone and clay-slate; so that it would be fruitless to dig for chalk in Durham, for magnesian limestone in Fife, or for coal in Perthshire. It would not be absurd, however, to dig for coal in Durham, because that mineral underlies the magnesian limestone ”

“ The red marl is so widely distributed in that part of England which lies between Lancashire and the southern coast of Devonshire, and is so frequently found in that district in the same geological position which it occupies in the northern and midland counties in alliance with the magnesian limestone (lying for instance in horizontal strata upon the inclined coal measures, and bounding them at their basset) that it might be expected in some part of its course to discover traces of the magnesian rock. ”

“ At Stockport the Permian strata are stated by Mr. Hull to be more than 1,500 feet thick.
In Yorkshire, Nottinghamshire, and Derbyshire, the Permian strata are stated by Mr. Aveline to be divided into two chief groups: the Roth-liegende, of no great thickness, and the Magnesian Limestone series; the latter being the largest and most important member of the Permian series in the northern counties of England. The Magnesian Limestone consists there of two great bands, separated by marls and sandstone, and quarried for building and for lime. ”

“ In texture, a few limestones are compact, some oolitic, many cellular, the cells lined with crystallised carbonate of lime, a large proportion of a fine sandy grain, some quite powdery, with crystallised balls included; and in Nottinghamshire, considerable tracts yield granular crystallised limestones. Near Sunderland laminated rocks are really of sparry texture. Strings and plates of spar are very common, and render buildings of the magnesian limestone very irregular in their decay, from the unequal perishing of the stone between the ribs of spar. ”

“ It may seem at first very remarkable that the basis of the limestone conglomerate should be in one place merely a common limestone, and that in another spot, not far distant, it should contain a considerable proportion of magnesia. ”

“ The Magnesian Limestone, from 100 to 500 feet in thickness, forms a stripe of generally poor thin soil from Durham to Nottingham, capable of improvement as arable land by high farming, but bearing naturally a poor pasture, intermingled with sometimes magnificent furze. ”

“ Where we see a particular assemblage of strata, as the limestone conglomerate, manifestly of the same formation, exhibiting in several parts of its extent changes of composition altogether depending upon a difference in its chemical constitution, it is impossible to explain such an occurrence but by supposing that the fluid menstruum must have contained in different places different chemical ingredients. Every geologist will figure to himself illustrations of the want of uniformity in the same rock formation. ”

“ In some portions of Europe dolomite areas are sandy deserts, whose sand consists of weathered dolomite, so pure as to offer no adequate supply of mineral food to plants. In the United States, magnesian limestones underlie the “barrens” of several States and thus seem to justify their European reputation of being poor soil-formers. The exact cause of this difference is not fully understood, for at first sight it is not clear why the presence of the magnesian carbonate should interfere with the well-known beneficial effects of the lime compound. ”

“ The impurities of the clay, the iron and silica which it contains, may run as low as one-third of one per cent. The large per cent of carbonate of magnesia present makes it a cool lime, slow to slack and slow to set, and it is to such limes that architects, masons, and plasterers now invariably give preference over the so-called hot limes burned from non-magnesian limestones. The hardness and durability of mortars made from the LeClaire rock limes approaches that of cement, and after thirty-five or forty years of weathering, joints in mason work seem almost as fresh as when first struck. ”

“ Magnesian rocks as a whole are practically found to be not specially desirable soil-formers, even in the form of magnesian limestones. They do not even, as a rule, contain as many useful accessory minerals as are commonly found in limestones. Moreover, an excess of magnesia over lime is injurious to most crops, as is shown later (chapt. 18) .
The Zeolites.—Zeolites may be defined as hydro-silicates [Pg 37] containing as bases chiefly lime and alumina, commonly together with more or less of potash and soda, more rarely magnesia and baryta. ”

“ The various calcareous deposits in the mountain limestone, magnesian, oolite, and chalk periods, would imply very different qualities in the condition of the ocean; an infusion or abstraction of ingredients as favorable to the existence of one kind of animal life as they would be destructive of another. A period of great plutonic action, too, when vast masses of melted matter, charged with metallic and other substances, were poured over the bed of the sea, could not fail to have considerable influence upon many of the inhabitants of the deep ”

“ Much of it decomposes when exposed to air and moisture, and forms a good mould, whenever the descent of ground permits an accumulation of earth. It is not improbable, that in most places of the Staten-Island hills, when magnesia constitutes a considerable ingredient of the rock, it will be found saturated with carbonic acid, obviating the objection to common magnesian minerals in agriculture.
The minerals observed on the surface of the northeast part of this chain of hills are, secondary greenstone, asbestoid, sandstone, granite, and gneiss, sparingly scattered in rolled masses. ”

“ A common case arises where a granite magma, perhaps already bearing crystals, is intruded, under pressure operating from a distance, into a well-bedded series of sedimentary rocks. The sediments open up like the leaves of a book and admit the invader along their planes of stratification. Even limestone may thus become interlaminated with an igneous rock, - 122 - just as basalt has been known to separate the annual rings of trees involved in it. ”

“ A magma may be modified by the rocks into which it intrudes, so that a "basic" fluid may become charged with silica from a sandstone, the product crystallising as a granite; while an "acid" fluid may become so charged with limestone that diorite ultimately results. A. Harker [80] has discussed both theories clearly, with a strong leaning to the acceptance of magmatic differentiation in the cauldron as the only important cause of variation. ”

“ Owing to the great igneous and volcanic activity at the close of the deposition of the carboniferous system of strata, the coal-measures exhibit what are known as faults in abundance. The mountain limestone, where it outcrops at the surface, is observed to be much jointed, so much so that the work of quarrying the limestone is greatly assisted by the jointed structure of the rock. ”

“ As it is evident that no foreign ingredient could penetrate the substance of the rock in its present hardened condition, so as to unite with the other constituents, and diffuse itself uniformly through the mass, it seems necessary for Von Buch's hypothesis to suppose the limestone to have previously been at least softened by the heat, which occasioned the sublimation of the magnesia. ”

“ The folding of the sediments merges into intrusions of magma in the southern Appalachians. Here arose the granite problem on a tremendous scale, which is repeated in our Ascutney Mountain in Vermont. What it was doing under the bottom of those vast fields of limestone from Ohio to Illinois we have no idea. No more do we know what is doing under the vast fields of lime and red ooze at the present bottoms of the deep oceans. But we do know that fire-made rock squirts up under all sea-laid sediments which anyone has ever studied on islands or continents. ”

“ On the outside of this circle, of 25,000 miles it is only reasonable to expect an enormous strain. The abrasion of limestone found in huge masses will, by process of heat, convert them into lime. The contact with water, universal throughout the Earth, will start the volcano, which by slaking, this small amount of rock converted into lime will generate a heat that may ignite and produce more lime, or reach other combustibles, which may be set on fire by this; or when in contact with other substances, this would lead to reservoirs of oil and gas, and deposits of coal and sulphur. ”

“ This problem brings us to the threshold of astronomy, for limestone is metallic in character, susceptible therefore of fusion, and may have formed a part of the materials of our earth, even in an incandescent state, when the worlds were forming. But though this investigation as to the origin of lime does not belong either to the naturalist or the geologist, its suggestion reminds us that the time has come when all the sciences and their results are so intimately connected that no one can be carried on independently of the others. ”