Matrix (geology)

“ There seems, then, no escape from the admission that neither physical geology, nor paleontology, possesses any method by which the absolute synchronism of two strata can be demonstrated. All that geology can prove is local order of succession. It is mathematically certain that, in any given vertical linear section of an undisturbed series of sedimentary deposits, the bed which lies lowest is the oldest. ”

“ Stratigraphy and paleontology are concerned with the sedimentary and life history of the earth. The determination of the ages of the earth's strata and of the conditions of their deposition is required in the practice of economic geology. For example, a detailed knowledge of the succession of rocks and their ages, as determined by fossils and other stratigraphic evidence, is vital to the interpretation of conditions in an oil or coal field, and to the successful exploration and development of its deposits. ”

“ It was remarked that the same species of organic remains cannot be traced horizontally, or in the direction of the planes of stratification for indefinite distances. This might have been expected from analogy; for when we inquire into the present distribution of living beings, we find that the habitable surface of the sea and land may be divided into a considerable number of distinct provinces, each peopled by a peculiar assemblage of animals and plants. In the Principles of Geology, I have endeavoured to point out the extent and probable origin of these separate divisions ”

“ Age of each set of metamorphic strata twofold — Test of age by fossils and mineral character not available — Test by superposition ambiguous — Conversion of dense masses of fossiliferous strata into metamorphic rocks — Limestone and shale of Carrara — Metamorphic strata of modern periods in the Alps of Switzerland and Savoy — Why the visible crystalline strata are none of them very modern — Order of succession in metamorphic rocks — Uniformity of mineral character — Why the metamorphic strata are less calcareous than the fossiliferous. ”

“ Geological maps belong strictly to Descriptive Geology; they are free from those wide and doubtful speculations which form so large a portion of the earlier geological books. Yet even geological maps cannot be usefully or consistently constructed without considerable steps of classification and generalization. When, in our own time, geologists were become weary of controversies respecting theory, they applied themselves with extraordinary zeal to the construction of stratigraphical maps of various countries ”

“ Hidden under the farm vegetation or masked by the woods are scattered outcroppings of rock which have been the basis of the geologist’s judgment in preparing the map. Experience shows that in order to bridge the wide gap between the geology in the landscape and the patches of color upon the map something more than mere examination of the colored sheet is necessary. ”

“ With the cretaceous system ends the long series of deposits which are, by general consent, ranked as strata of the secondary periods of geology. In reviewing the successive secondary formations, from the red sandstones to the green sand, and from the mountain limestone to the chalk, it is impossible not to recognise, on a great scale, the gradual change of the physical conditions of the globe which took place during this period. Mineralogically, the rocks successively deposited deviate more and more from the types of the primary strata ”

“ To illustrate this, let the subjoined diagrams represent portions of clay slate and grauwacke slate, alike in all respects of structure, except the nature and direction of the lamination, D being in each a plane of stratification. In grauwacke slate (No. 37.) the laminæ of deposition show on all the vertical planes, being all parallel or nearly so to the plane of stratification; in clay slate laminæ of deposition are not seen ”

“ A species which has once died out does not seem ever to have reappeared.
4. When the order of succession of organic remains among the stratified rocks has been determined, they become an invaluable guide in the investigation of the relative age of rocks and the structure of the land. Each zone and formation, being characterized by its own species or genera, may be recognized by their means, and the true succession of strata may thus be confidently established even in a country wherein the rocks have been shattered by dislocation, folded, inverted or metamorphosed. ”

“ But it is possible that after a bone has gone on losing its animal matter up to a certain point, it may then part with no more so long as it continues enveloped in the same matrix, so that if all the bones have lain for many thousands of years in a particular soil, they may all have reached long ago the maximum of decomposition attainable in such a matrix. ”

“ Fossils as means of correlation.—While stratigraphy was thus, in the earliest stages, the main reliance in determining the order of events, and biology was the chief gainer, in the end stratigraphy received ample compensation, if indeed it did not become the greater beneficiary; for at no known and accessible place is there a complete succession of sedimentary beds. There are great series here and there, but their connections with one another are more or less concealed by surface formations or water-bodies. ”

“ A succession of strata indicates a succession of time for their formation; and the change from one species of stratum to another placed upon it, indicates a change of cause. Thus is the mass of our continents the product of successive operations, during which the producing causes have undergone successive changes. We see, moreover, that many of these strata contain the remains of animals; and that in some successive strata these organized bodies are of different species. ”

“ This mode of accounting for the origin and formation of Stratified Rocks constitutes in a manner the framework that supports and binds together the whole system of Geology. If it be once fairly established, Geology is entitled to take high rank as a Physical Science. If on the contrary it should prove to be without foundation, then Geology is no longer a science, but a dream. Moreover, it is this theory of stratification which, from the first, has brought Geology into contact with Revelation. ”

“ Such a system of classification is not only recommended by its greater clearness and facility of application, but is also best fitted to strike the imagination by bringing into one view the contemporaneous revolutions of the inorganic and organic creations of former times. For the sedimentary formations are most readily distinguished by the different species of fossil animals and plants which they inclose, and of which one assemblage after another has flourished and then disappeared from the earth in succession. ”

“ But we have not yet done with this part of our investigation. The argument from geology is based on the assumption that the chronological order of the earth's layers has been determined at least with great approximation to certainty, so that we may say with some assurance that this layer of limestone or sandstone is of earlier, that, of later origin. As a matter of fact, the textbooks do treat the various "ages" of geology as if they corresponded to certain strata of the earth's crust. But by what method is the age of the various layers determined? ”

“ To the fact of the elevation of the strata, the study of geology is much indebted. The stratified form of a great proportion of the earth's surface, gives to minerals that organization and regularity, which makes their disposition an object of science, and their inclined position serves to bring that organization into view, from far greater depths than we can ever reach by artificial excavations. ”

“ The fossiliferous rocks are divided into seven systems, which are readily distinguished by the order of superposition, lithological characters and organic remains. These systems are the Silurian, the Old Red Sandstone, the Carboniferous, the New Red Sandstone, the Oölitic, the Cretaceous, and the Tertiary systems. There is also an eighth system now in process of formation.
It is the opinion of some geologists that there is another system situated between the metamorphic rocks and the silurian system. ”

“ But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed on the earth, be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory. The explanation lies, as I believe, in the extreme imperfection of the geological record. ”

“ But an experienced geologist can rarely be deceived by these exceptional cases. When he finds that the strata are fractured, curved, inclined, or vertical, he knows that the original order of superposition must be doubtful, and he then endeavours to find sections in some neighbouring district where the strata are horizontal, or only slightly inclined. Here, the true order of sequence of the entire series of deposits being ascertained, a key is furnished for settling the chronology of those strata where the displacement is extreme. ”

“ Every good Geological Map ought to explain itself. It ought, in fact, to tell its own story regarding the features of the country it represents, and the rocks and formations of which the region is constructed; and if every person was acquainted with the principles of geology, and had been properly instructed in the plan according to which Geological Maps are prepared, no explanation would be required. ”

“ The elements of structure are set forth in a more elaborate form in structural geology when slaty structure, lode structure and stratified structure are the themes, and where flexures, faults, fractures and displacements are set forth in describing the structure of mountains, plateaus, hills and plains as slates, lodes and strata, giving figure to the topographic features and the endless variety and beauty of the topographic landscape. ”

“ The new school of geologists included men like William Phillips, Conybeare, Sedgwick, Buckland, De la Beche, Fitton, Mantell, Webster, Lonsdale, Murchison, John Phillips and others, who laid the foundations of British stratigraphical geology. ”

“ When, however, the second criterion, namely, the fossil content of the strata, is used in direct connection with the order of superposition, we have the real basis for determining the relative ages of strata for all parts of the earth. ”

“ There are endless variations in the figures described by the basset-edges of the strata, according to the different inclination of the beds, and the mode in which they happen to have been denuded. One of the simplest rules, with which every geologist should be acquainted, relates to the V-like form of the beds as they crop out in an ordinary valley. First, if the strata be horizontal, the V-like form will be also on a level, and the newest strata will appear at the greatest heights. ”

“ In many places where a vertical section is exposed to view, the phenomenon of stratification may be distinctly recognized. The upper part of the deposit belonging to each year is composed of earth of a lighter color than the lower part; and the whole forms a distinct layer of hardened clay, which may be easily separated from those above and below. This formation, therefore, corresponds exactly with those strata of shale which we so often meet with in the Crust of the Earth. ”

“ When we discover a constant and regular assemblage of organic Remains, commencing with one series of strata, and ending with another, which contains a different assemblage, we have herein the surest grounds whereon to establish those Divisions which are called geological formations, and we find many such Divisions succeeding one another, when we investigate the mineral deposites on the surface of the Earth. ”

“ The fossiliferous strata, as they are generally termed, have been chronologically arranged in a series of formations, each of which is characterised by its own peculiar suites of fossils. Their relative age has been determined, as we have indicated above, by their fossils, and also by certain physical tests, the chief of these being superposition. It holds invariably true that a formation, A, found resting upon another series of strata, B, will always occur in precisely the same position, wherever these two deposits occur together. ”

“ A knowledge of the geology of the land is of the first importance; that is, not only a knowledge of the range and extent of each formation and its subdivisions, which may be called geographical geology, but also how far and to what extent the various lands do depend upon the substratum for their soil, and the local variations in the chemical or mineralogical character of the substrata themselves, and which may be called the differential geology of soils. ”

“ Now we have shown that in the earth's long history some regions are always being denuded of materials in order that these materials may be laid down as sediments elsewhere. These movements may be compared to those of a pair of scales, in which we are continually taking weight from the scale pan that is weighted in order to put it into the scale that is empty. The scale that is weighted is the land from which material -135- is being removed by the rains and the rivers; the scale that is empty is the sea, in which the eroded material is laid down to form beds and strata. ”