Very many facts are known by experience before the laws which unite these facts into system are embodied into science. The stratification of many rocks; the alternation of rocks of different nature; the peculiar positions of metallic veins; these and many other circumstances, which are now known in the shape of general laws of phenomena, must have been known in the mines and collieries and quarries of Europe from an early period of the middle ages. The quality and distribution of soils; the characteristic features of ranges of hills; the peculiarities of the origin and course of many rivers; these and other facts observable on the surface of the earth, which are now seen to depend on the peculiar qualities and positions of rocks below the surface, were formerly known as insulated facts, and, in some instances, may have suggested to such men as Packe, and Lister, and Evelyn, views of the earth's structure more conformable to modern philosophy than appear in their writings.
The naturalists of Italy, represented by Scilla, had begun to reason correctly on several points of the history of organic remains before our Woodward mixed truth and error in his 'Natural History of the Earth,' and threw into unprofitable discussions about the Deluge, the talent which had been awakened in England to contemplate facts which are the foundation of the highest geological laws. The glimpses of general truth which those early writers obtained constitute a considerable body of knowledge, and are far more worthy of a place in the history of English geology than the sounding speculations of Burnet, and Whiston, and even Whitehurst, great as are the merits in other respects of that remarkable author.
That the earth is stratified in parts near the surface was generally known to the writers on geology in the sixteenth century, and is indeed one of the leading phamomena which their hypotheses were framed to explain. That the strata, considered as definitely extended masses, were arranged one upon another in a certain settled order or series, nowhere appears as a law, even for a limited district, previous to the remarkable paper by John Strachey in the Phil. Trans., which gives the succession of strata in the coal district of Somersetshire (1719 and 1725). For here (1719) we have the coal series covered, and covered unconformably, by the red marl, lias and oolite; and (in 1725) the limits of the coal-field, between Mendip Hills on the south, Cotswold on the north-east, and Marlborough Downs or Salisbury Plain. In a section he represents, in their true order, chalk, oolites, lias, red marls and coal, and the metalliferous rocks. But there are glimpses of such a law in earlier writers. Thus Woodward, in one of several false assertions (to which his inconsiderate anxiety in support of a favourite doctrine led him), speaks of chalk as an upper stratum, and accounts for this circumstance by reason of its lightness as compared with other rocks. He even accounts for the occurrence of Echinodermata, &c. in the chalk, while different exuviae lie in other rocks, by the same rule of specific gravity, the lightest rocks having the lightest shells. This reasoning was ridiculous, but the passage is curious, as showing a certain amount of knowledge on a point which had been the least investigated. . . .
Until the appearance of an ' Essay on the Cause and Phaenomena of Earthquakes,' by the Rev. John Michell (Philosophical Transactions, 1760), there was nothing published of importance in the advancement of geology. The subject which Michell undertook to investigate, compelled him to look at the construction of the earth on a large scale, and to pass beyond the limits of Britain for illustrations. Accordingly we find him stating some classes of data, such as the general facts of stratification, the position of the strata, their horizontality under plains and acclinal rise toward mountain ridges, for the purpose of establishing a general conclusion, which is thus expressed:— "From this formation of the earth it will follow, that we ought to meet with the same kinds of earths, stones and minerals, appearing at the surface, in long narrow slips, and lying parallel to the greatest rise of any long ridges of mountains; and so, in fact, we find them." He gives as illustrations the regions of the Andes and the Sierra in South America, and the mountain ranges of North America, and then adds, "In Great Britain we have another instance to the same purpose, where the direction of the ridge varies about a point from due north and south, lying nearly from north by east to south by west. At considerable distances from large ridges of mountains the strata for the most part assume a situation nearly level, and in the mountainous countries are generally formed out of the lower strata; so the more level countries are generally formed out of the upper strata of the earth."
The author of these just and admirable generalizations became, in 1762, Woodwardian Professor at Cambridge, and held that appointment till about 1770. He then accepted the rectory of Thornhill, near Dewsbury in Yorkshire, and in his journeys to and from Cambridge crossed the rocks between the "coal strata of Yorkshire" and the "chalk." By these journeys he became sufficiently acquainted with the series of secondary formations in England to assist with his knowledge both Smeaton and Cavendish. . . . he information which Michell possessed must have produced a great influence on the progress of positive geology had he retained the Woodwardian Professorship. . . . . Whitehurst (publishing in 1777) quotes Michell's paper on earthquakes, but never alludes to his or any other scale of stratification; and that no British or foreign writer, not even a Woodwardian professor in the eighteenth century, published, employed, or in any manner alluded to, any such list! Whitehurst, though inferior to Michell in philosophical power, and not possessed of the same firm and appropriate idea of the earth's structure, has the merit of announcing more distinctly than any previous writer the law of the settled order of succession among the strata, which must ere this have been rather generally allowed. "The arrangement of the strata," he tells us, "in general is such, that they invariably follow each other, as it were, in alphabetical order . . .
We have now cleared the way to William Smith, who was born about the time when Michell quitted Cambridge, and acquired the first clear and consistent view of the series of stratification near Bath, just about the time when Smeaton published his chapter on water-cements. In a great degree self-educated, forced to struggle into notice in a laborious profession, unacquainted even with the names of Michell and Cavendish, the phaenomena which had caught the notice of Strachey in Somersetshire fixed the attention of the young man. But instead of supposing with Strachey, strata curved from the centre to the circumference of the earth, or looking with Michell at the Andes and the Sierra, or with Whitehurst expanding into propositions the limited experience of the miners of Derbyshire, he concentrates his attention on the general regularity of the strata near Bath (1790-91), broken only by the single case of unconformity between the red ground and the coal. He indulges no speculations of horizontal strata in plains and inclined strata in mountains, but seeing and proving as a local fact that the strata of Somerset have a general inclination to the east or south-east, turns all the energy of his mind to determine if a similar law applies in other districts, dwells for this purpose on every memory of his earliest years (1787-8-9), seizes every occasion of travelling which limited means permit, accepts with joy the opportunity of a long journey through England and Wales (1794), takes eager notes of every hill and every quarry, and returns satisfied that the surface of our island is formed on the edges of strata which are continuous for great areas, which succeed one another in a certain order, preserve approximately the same thickness and quality, produce similar soils, have similar uses, and affect in like manner the drainage, the elevation, the physical geography, and the whole aspect of the country. Once master of these ideas, he took them as the guiding-star, the one object of his life; illustrated them by models, maps and collections; deduced from them new methods of drainage, new principles of mineral surveying, new practices in engineering; and at length, after minute and repeated examinations, not only completed a Table of Stratification, and coloured maps, and arranged collections, such as never were conceived before, but arrived at further and more magnificent discoveries, of which scarcely the least indication can now, by the most scrutinizing search, be found in the records of earlier inquiry.
Accustomed to view the surfaces of the several strata which are met with near Bath uncovered in large breadths at once, Mr. Smith saw with the distinctness of certainty, that "each stratum had been in succession the bed of the sea;" finding in several of these strata abundance of the exuviae, of marine* animals, he concluded that these animals had lived and died during the period of time which elapsed between the formation of the stratum below and the stratum above, at or near the places where now they are imbedded; and observing that in the successively-deposited strata the organic remains were of different forms and structures—Gryphites in the lias, Trigoniae in the inferior oolite,- hooked oysters in the fuller's earth,—and finding these facts repeated in other districts, he inferred that each of the separate periods occupied in the formation of the strata was accompanied by a peculiar series of the forms of organic life, that these forms characterized those periods, and that the different strata could be identified in distant localities and otherwise doubtful cases by peculiar imbedded organic remains. [128-41]
Related material
- William “Strata” Smith (1769-1839): Geology and Coal
- Smith’s Explanation of His Map of Geological Strata in England and Wales
- A County-by-County Geological Description of England’s Counties
Bibliography
Philips, John. Memoirs of William Smith, LL.D., Author of the “Map of the Strata and Wales. London: John Murray, 1844.
Smith, William. A Memoir to the Map and Delineation of Strata of England and Wales. London: John Cary, 1815.
Created 9 September 2018