fauna) of any set of strata, we can determine whether these strata are of lacustrine, of estuarine, or of marine formation. Again, we see how unstratified rock-masses are produced by volcanic eruption, and how the earth's crust is rent and fissured by earthquake convulsions, and we rightly infer that all unstratified rocks are of igneous origin, and that the fractures and faults among the older strata have been brought about by subterranean disturbance. In this way we get glimpses of the past conditions of the globe-the distribution of its lands and waters, the kind of plants and animals by which it was successively peopled, and in the main of its geographical conditions and appointments. And by arranging the whole in chronological order (from the deposits of yesterday to the deepest rocks we can reach) we get something like a connected history of the earth through its ancient, medieval, and recent aspects, just as we get of human history through its ancient, medieval, and modern developments.

But while engaged in this task it will be found that ancient changes and ancient rock-formations are far less evident and of much more difficult interpretation than those of recent date, and that this difficulty goes on increasing as we descend in the earth's crust until we reach a stage when everything becomes obscure, and all the rocks are converted into homogeneous, or all but homogeneous, crystalline masses. The clays, muds, marls, sands, and gravels, which form the superficial accumulations, bear obvious evidence of the manner in which they have been aggregated, and of the conditions under which their imbedded plants and animals lived-and the sandstones, shales, ironstones, coals, and limestones of the older strata, with their enclosed fossils, reveal in a similar way the general facts of their formation but in these deepest rocks, where stratification is in a great measure effaced, and not a trace of plant-life or animal-life

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can be discovered, the geological record ceases, and all beyond becomes mere matter of guess-work and conjecture. It is important, then, for the young geologist to know that the field of his labours is restricted, or all but restricted, to the stratified fossiliferous rocks. In these, with their imbedded fossils, he sees the sediments of former lakes, seas, and estuaries, and can infer with some degree of certainty as to the former distributions of sea and land, and the life by which they were peopled. In these, with their accompanying volcanic products-their fractures, upheavals, and depressions, he can trace the physical agencies of bygone periods, and compare them with the present. But in the old crystalline rocks, where the record of life and geographical aspect is obliterated, he can decipher with certainty no further, and must close his labours as an inductive geologist.

The scope of geology as a science of observation and deduction is restricted, therefore, to the stratified and accessible crust. In this, built up, modified and re-modified a thousand times by the forces now operating around us, we can trace a long and wonderful history of physical and vital mutation; and it is to the perfection of this history in all that has reference to geographical aspect, operative cause, and vital progress, that the modern geologist directs his attention. All that relates to the primordial condition of the earth, and to its origin and evolution as a member of the solar system, belongs to cosmogony and astronomy, and not to geology; and however attractive it may be as a speculation, it cannot be admitted among the observed facts and legitimate deductions of our science. It is of paramount importance, then, that in geology, as in other departments of science, the student should thoroughly understand the aim and scope of his subject, concentrating his energies on what seems fairly attainable, rather than dissipating his thought

on what belongs to another theme, if indeed it be not altogether unapproachable.

The aim of geology being to read the history of the Earth through its rocks and fossils, and its scope being restricted to that portion of the crust which gives evidence of the causes by which it was produced and the conditions accompanying its formation, the student has before him a task which, however arduous, is at least intelligible, and hopefully within his reach. In his surveys, maps, and sections he can separate the younger from the older strata— can say whether they have been deposited in lakes, in seas, or in estuaries—can tell the nature of the plants and animals imbedded within them-can indicate the climatic conditions under which these had lived and flourished-show the changes which these strata have undergone by contemporaneous or subsequent volcanic activity-and in the main depict the geographical features which the region of his study has successively undergone. The successive features he may call stages, or formations, or systems; and by arranging them in chronological sequence he gains a view of the long line of world-history similar to that which the historian arrives at by the study of modern, medieval, and ancient populations. In reading this long history he perceives that the earth's crust is in a state of incessant change that the forces which act are ever the same in kind though differing in degree that in the plants and animals there has been a progress in the main from lower to higher forms-and that all the changes, whether of a physical or of a vital nature, have ever been in accordance with certain modes and processes, or, in other words, under the unerring direction of fixed and enduring Law. Were it not so, observation might be deceiving us at every turn, and we could never hope to arrive at anything like certainty in our deductions.

Such being the aim and scope of geology, a very cursory

inquiry will suffice to show that its bearings, scientific and practical, are of commensurate importance. As a theme requiring minute observation, discriminating reflection, and the power of logically tracing results to their producing causes, its intellectual bearings are of the highest order; while the influence of its deductions on botany and zoology, on the science of life in general, and on our conceptions of time and the operation of natural law, have been such as to mark within the last half-century an era altogether new in our scientific convictions. What ennobling views of creation, of time, change, continuity, and undeviating order, has the study of geology imparted, compared with the restricted notions of our forefathers! what exalted conceptions of divine prescience and method compared with the fitful, temporary, makeshift plans that were formerly ascribed to the Creator! Nor are its practical or economic bearings less varied and valuable. Arranging as it does the rocky crust into stages and formations, it can point with precision to the sites of the various rocks, minerals, and metals, to their scarcity or abundance, and thus confer on the miner, the engineer, builder, and farmer, information of direct practical utility. And when we reflect how much mankind are dependent on the minerals and metals for all that relates to comfort, civilisation, and progress, it will be readily granted that the economic bearings of geology are fully commensurate with those that are scientific or intellectual.

Such is a brief indication of the aim, scope, and bearing of geological inquiry. Under the operation of certain forces we see this world of ours undergoing incessant change, and each change marked by its own peculiar rocks and their relations, and believing in the fixed and enduring nature of these forces, we seek to discover the changes it

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has undergone in time past by examining the rock-formations of the crust; or, by reversing the order, we try from the earliest traces of change in the rocky crust to read the history of the earth onwards and upwards to the changes now going on, and the rocks that are now forming around In either case we believe in the fixity and uniformity of nature's operations, and further believe that every period and change leaves its own record of waste and reconstruction in the crust, together with some memorials of the plant-life and animal-life that peopled the surface during its continuance. Geology is thus the history of our planet read through its rocks and fossils; and where the former contain no fossils, nor exhibit by their structure and texture any evidence of the conditions under which they were formed, then the task of inductive geology ceases, and the primordial state of our globe is handed over to the physicist and astronomer. The aim and scope of geology being clear-and what an ambitious aim, and how vast the field of inquiry the bearings of the science, theoretical and practical, are readily understood and easily appreciated. No knowledge can bear more directly on the industry of a country so long as the minerals and metals are indispensable to mechanical achievement and progress; no science of recent times has spread so rapidly or influenced so broadly our ideas of time, change, continuity, and creational progression.