CHAPTER II. FORMATION OF SYSTEMATIC DESCRIPTIVE Geology. Sect. 1.-Discovery of the Order and Stratification of the Materials of the Earth. THAT the substances of which the earth is framed are not scattered THAT and mixed at random, but possess identity and continuity to a considerable extent, Lister was aware, when he proposed his map. But there is, in his suggestions, nothing relating to stratification; nor any order of position, still less of time, assigned to these materials. Woodward, however, appears to have been fully aware of the general law of stratification. On collecting information from all parts, "the result was," he says, "that in time I was abundantly assured that the circumstances of these things in remoter countries were much the same with those of ours here: that the stone, and other terrestrial matter in France, Flanders, Holland, Spain, Italy, Germany, Denmark, and Sweden, was distinguished into strata or layers, as it is in England; that these strata were divided by parallel fissures; that there were enclosed in the stone and all the other denser kinds of terrestrial inatter, great numbers of the shells, and other productions of the sea, in the same manner as in that of this island."1 So remarkable a truth, thus collected from a copious collection of particulars by a patient induction, was an important step in the science. These general facts now began to be commonly recognized, and followed into detail. Stukely the antiquary (1724), remarked an important feature in the strata of England, that their escarpments, or steepest sides, are turned towards the west and north-west; and Strachey (1719), gave a stratigraphical description of certain coal-mines near Bath. Michell, appointed Woodwardian Professor at Cambridge 1 Natural History of the Earth, 1723. 2 Itinerarium Curiosum, 1724. 4 Phil. Trans. 1719, and Observations on Strata, &c. 1729. Fitton, Annals of Philosophy, N. S. vol. i. and ii. (1832, '3), p. 157. in 1762, described this stratified structure of the earth far more distinctly than his predecessors, and pointed out, as the consequence of it, that "the same kinds of earths, stones, and minerals, will appear at the surface of the earth in long parallel slips, parallel to the long ridges of mountains; and so, in fact, we find them." Michell (as appeared by papers of his which were examined after his death) had made himself acquainted with the series of English strata which thus occur from Cambridge to York;—that is, from the chalk to the coal. These relations of position required that geological maps, to complete the information they conveyed, should be accompanied by geological Sections, or imaginary representations of the order and mode of superpositions, as well as of the superficial extent of the strata, as in more recent times has usually been done. The strata, as we travel from the higher to the lower, come from under each other into view; and this out-cropping, basseting, or by whatever other term it is described, is an important feature in their description. It was further noticed that these relations of position were combined with other important facts, which irresistibly suggested the notion of a relation in time. This, indeed, was implied in all theories of the earth; but observations of the facts most require our notice. Steno is asserted by Humboldt to be the first who (in 1669) distinguished between rocks anterior to the existence of plants and animals upon the globe, containing therefore no organic remains; and rocks super-imposed on these, and full of such remains; "turbidi maris sedimenta sibi invicem imposita." Rouelle is stated by his pupil Desmarest, to have made some additional and important observations. "He saw," it is said, "that the shells which occur in rocks were not the same in all countries; that certain species occur together, while others do not occur in the same beds; that there is a constant order in the arrangement of these shells, certain species lying in distinct bands."" Such divisions as these required to be marked by technical names. A distinction was made of l'ancienne terre and la nouvelle terre, to which Rouelle added a travaille intermédiaire. Rouelle died in 1770, having been known by lectures, not by books. Lehman, in 1756, claims for himself the credit of being the first to observe and describe correctly the structure of stratified countries; being ignorant, pro 5 Phil. Trans. 1760. • Essai Géognastique. 7 Encyl. Méthod. Geogr. Phys. tom. i. p. 416, quoted by Fitton as above, p 159. bably, of the labors of Strachey in England. He divided mountains into three classes ;* primitive, which were formed with the world;those which resulted from a partial destruction of the primitive rocks; -and a third class resulting from local or universal deluges. In 1759, also, Arduine, in his Memoirs on the mountains of Padua, Vicenza, and Verona, deduced, from original observations, the distinction of rocks into primary, secondary, and tertiary. The relations of position and fossils were, from this period, inseparably connected with opinions concerning succession in time. Odoardi remarked," that the strata of the Sabapennine hills are unconformable to those of the Apennine, (as Strachey had observed, that the strata above the coal were unconformable to the coal;") and his work contained a clear argument respecting the different ages of these two classes of hills. Fuchsel was, in 1762, aware of the distinctness of strata of different ages in Germany. Pallas and Saussure were guided by general views of the same kind in observing the countries which they visited: but, perhaps, the general circulation of such notions was most due to Werner. Sect. 2.-Systematic form given to Descriptive Geology.-Werner. WERNER expressed the general relations of the strata of the earth by means of classifications which, so far as general applicability is concerned, are extremely imperfect and arbitrary; he promulgated a theory which almost entirely neglected all the facts previously discovered respecting the grouping of fossils,-which was founded upon observations made in a very limited district of Germany,—and which was contradicted even by the facts of this district. Yet the acuteness of his discrimination in the subjects which he studied, the generality of the tenets he asserted, and the charm which he threw about his speculations, gave to Geology, or, as he termed it, Geognosy, a popularity and reputation which it had never before possessed. His system had asserted certain universal formations, which followed each other in a constant order;-granite the lowest,-then mica-slate and clay-slate;-upon these primitive rocks, generally highly inclined, rest other transition strata ;-upon these, lie secondary ones, which being more nearly horizontal, are called flötz or flat. The term formation, Lyell, i. 70. 10 Ib. 74. VOL. II-33. • Ib. 72. 11 Fitton, p. 157. which we have thus introduced, indicating groups which, by evidence of all kinds, of their materials, their position, and their organic contents, are judged to belong to the same period, implies no smal amount of theory: yet this term, from this time forth, is to be looked upon as a term of classification solely, so far as classification can be separately attended to. Werner's distinctions of strata were for the most part drawn from mineralogical constitution. Doubtless, he could not fail to perceive the great importance of organic fossils. "I was witness," says M. de Humboldt, one of his most philosophical followers, "of the lively satisfaction which he felt when, in 1792, M. de Schlotheim, one of the most distinguished geologists of the school of Freiberg, began to make the relations of fossils to strata the principal object of his studies" But Werner and the disciples of his school, even the most enlightened of them, never employed the characters derived from organic remains with the same boldness and perseverance as those who had from the first considered them as the leading phenomena: thus M. de Humboldt expresses doubts which perhaps many other geologists do not feel when, in 1823, he says, "Are we justified in concluding that all formations are characterized by particular species? that the fossilshells of the chalk, the muschelkalk, the Jura limestone, and the Alpine limestone, are all different? I think this would be pushing the induction much too far."12 In Prof. Jamieson's Geognosy, which may be taken as a representation of the Wernerian doctrines, organic fossils are in no instance referred to as characters of formations or strata. After the curious and important evidence, contained in organic fossils, which had been brought into view by the labors of Italian, English, and German writers, the promulgation of a system of Descriptive Geology, in which all this evidence was neglected, cannot be considered otherwise than as a retrograde step in science. Werner maintained the aqueous deposition of all strata above the primitive rocks; even of those trap rocks, to which, from their resemblance to lava and other phenomena, Raspe, Arduino, and others, had already assigned a volcanic origin. The fierce and long controversy between the Vulcanists and Neptunists, which this dogma excited, does not belong to this part of our history; but the discovery of veins of granite penetrating the superincumbent slate, to which the controversy led, was an important event in descriptive geology. Hutton, the 12 Gissement des Roches, p. 41 author of the theory of igneous causation which was in this country opposed to that of Werner, sought and found this phenomenon in the Grampian hills, in 1785. This supposed verification of his system "filled him with delight, and called forth such marks of joy and exultation, that the guides who accompanied him were persuaded, says his biographer," that he must have discovered a vein of silver or gold."" Desmarest's examination of Auvergne (1768) showed that there was there an instance of a country which could not even be described without terms implying that the basalt, which covered so large a portion of it, had flowed from the craters of extinct volcanoes. His map of Auvergne was an excellent example of a survey of such a country, thus exhibiting features quite different from those of common stratified countries.15 The facts connected with metalliferous veins were also objects of Werner's attention. A knowledge of such facts is valuable to the geologist as well as to the miner, although even yet much difficulty attends all attempts to theorize concerning them. The facts of this nature have been collected in great abundance in all mining districts; and form a prominent part of the descriptive geology of such districts; as, for example, the Hartz, and Cornwall. Without further pursuing the history of the knowledge of the inorganic phenomena of the earth, I turn to a still richer department of geology, which is concerned with organic fossils. Sect. 3.-Application of Organic Remains as a Geological Character. -Smith. ROUELLE and Odoardi had perceived, as we have seen, that fossils were grouped in bands: but from this general observation to the execution of a survey of a large kingdom, founded upon this principle, would have been a vast stride, even if the author of it had been aware of the doctrines thus asserted by these writers. In fact, however, William Smith executed such a survey of England, with no other guide or help than his own sagacity and perseverance. In his employments as a civil engineer, he noticed the remarkable continuity and constant order of the strata in the neighborhood of Bath, as discriminated by their fossils; and about the year 1793, he drew up a Tabular View of the 13 Playfair's Works, vol. iv. p. 75. 14 Lyell, i. 90. |