served as the basis of many later hypotheses which contain no more information. The Pythagorean doctrine of the intermutations of substance, and repeated revolutions in the nature of all created things, of which this is urged as an example, has not a little resemblance to some of Dr. Hutton's speculations on cosmogony, whilst in Ovid's description of chaos, we really seem to behold the germ of a Wernerian theory.

We may pass the centuries of darkness which succeeded the splendid æra of Rome, and fix our attention on times more approaching our own. The discoveries of Newton, in celestial mechanics, introduced a new order of inquirers concerning the history of the earth; but, unhappily, few of them followed the steps of their illustrious leader. The" theories," as they were arrogantly termed, of Burnet, Whiston, Woodward, and Buffon, are now remembered only as the splendid errors of illustrious men, and the systematic hypothesis of Whitehurst, though far better supported by the practical knowledge of its author, has shared the same unregretted fate. To rank with these neglected dreams, the respected opinions of Hutton and Werner, would be unjust: the former, a man of capacious intellect and original genius, has combined in his system much that is excellent and much that is extravagant; but its errors have been corrected by the progress of inquiry, and its truths illustrated even by his opponents. Werner's fame rests secure on accurate observation and sagacious generalization of facts. From an examination of a small tract of country, he deduced principles which are found to be universally applicable. He first taught that the earth is constructed after a regular plan, and composed, near the surface, of rocks laid on one another, in a constant order of succession. His theoretical views, though zealously embraced by his numerous disciples, were of little value, and rather obscured the real utility of his practical system.

Geologists have commonly placed Mr. Smith in comparison with Werner; and have agreed that in England one was accomplishing what occupied the attention of the other in Germany, and that both were unconsciously acting on the same plan, and producing the same results. This is strictly true as far as relates to their practical opinions; but

Mr. Smith is no theorist in the ordinary sense of the word. His whole life has been spent in practical researches, to prove the truth, and extend the benefit, of those general laws of structure which he was the first to promulgate in England. Besides discovering, at nearly the same period as Werner, the principle of the arrangement of secondary strata, he added the important doctrine, that organic fossils are distributed in the earth according to regular laws, and may be employed to discriminate and identify the rocks. Werner and Smith are, therefore, the leaders of the modern school of geology, and whilst every fresh investigation illustrates the truth of their general principles, their names will be honoured with increasing respect, though every “theory" should be forgotten.

The methodical developement of first principles in geology, attempted in the following pages, is the result of repeated reflections on the subject, for the purpose of public instruction. It is a condensed abstract of parts of my lectures. Hoping that this account of the strata of the Yorkshire coast would be read by others besides professed geologists, I thought it desirable to furnish them with a plain distinct introduction to the science, in order to avoid obscurity and tedious repetition.

Formerly, the materials near the surface of the earth were thought to be every where alike, just as agriculturists now speak of the vegetable mould; and the internal parts were supposed to be a mere heap of minerals confusedly blended together: a very little experimental investigation was sufficient to overthrow so groundless a notion. One district has beneath the surface, chalk; another, oolitic limestone; a third, coal; a fourth, granite; and these are never mixed or confounded together; so that the most careless observer finds himself constrained to admit that not disorder, but method, appears in the situation of different rocks.

A person proceeds from London to North Wales. After passing low diluvial plains about London, he climbs, by a long slope, the chalk-hills of Oxfordshire and Berkshire; then crosses vales of clay and sandstone, ascends a range of oolitic limestone; traverses wide plains of blue and

red marl; arrives in districts where coal, iron, and limestone abound; and finally sees Snowdon composed of slate. And if, in proceeding from London to the Cumberland lakes, he finds the same succession of low plains, chalk-hills, clay vales, oolitic limestone ranges, blue and red clays, coal, iron, and limestone tracts, succeeded by the slate rocks which compose the well-known summit of Skiddaw, will he not conclude that something beyond mere chance has brought together these rocks in such admirable harmony? Will he not have reason to conjecture, that, in the interior of the earth, regularity of arrangement must prevail?

To such a conclusion we are forcibly impelled by exploring the relative position of rocks, as it is displayed in wells, quarries, and mines, the works of human industry, or laid bare in cliffs and ravines by the hand of nature. Here every one has seen the rocks formed in layers or tabular masses, placed one upon another, like the leaves of a book. These layers are called strata.

The sea-coast of Yorkshire affords excellent opportunities of examining into this matter; for there cliffs of great altitude, in prominent and accessible situations, are composed of several distinct layers of rock, which are piled one upon another in a regular order, preserve a definite thickness, and appear under the same circumstances in many distant places. But though one tract of country exceeds another in opportunities of this nature, yet the principle of stratification among rocks is confined to no country; for whether in the new or the old world, in continents or in islands, it is so remarkable and so constant, that colliers sink deep pits, and miners undertake expensive levels, in full confidence that no exception to its generality will affect the success of their enterprises. It is not a speculative truth, but a practical law of nature, and is, probably, the fact of most extensive influence in the whole system of geology.

The Wernerian school of geology held it to be a universal law of structure, and even Cuvier says, "All rocks are stratified." But such expressions are incorrect. How can the term strata be applied to basalt,

porphyry, and other unconformed masses? That granite is sometimes internally stratified, has been asserted, an appearance I never witnessed,—but every geologist knows abundance of examples in which it displays no trace of such a structure. These rocks, and some few others, are exceptions to the law of stratification; and if, as appears probable, their origin is different from that of stratified rocks, we need not wonder that they assume other modes of arrangement. But, neglecting these particular rocks, it is certain that stratification is the most general phenomenon hitherto discovered by geologists. Recognised by observers of different opinions, and in opposite quarters of the globe, it well deserves to be considered a fundamental doctrine. Let us inquire how these strata are combined in the crust of the earth; for so, perhaps, we may best designate the very limited depth to which it has been explored by human enterprise and science.

To ascertain the manner in which strata are placed in the crust of our globe, is certainly the great object of practical geology. The first rudiments of this knowledge should be early implanted in the mind of the student, by leading him to the contemplation of some well-marked natural section. Let him visit the sea-coast, and observe for himself whether or not the following proposition is true.

That, in a local tract, strata are superimposed on one another in a certain constant order of succession, like the leaves of a book.

Let us take the Yorkshire coast for an example. (See the Section.) Gristhorpe cliff is crowned by calcareous sandstone rocks, which lie upon a thick argillaceous stratum; under this is a brown ferruginous rock; and still lower is a thin calcareous layer full of fossils. The same calcareous sandstone is found on the top of Red cliff, and it rests in the same manner upon the argillaceous stratum, brown rock, and fossil bed. In Scarborough castle hill, the same calcareous sandstone, argillaceous stratum, brown rock, and fossil bed, occur in the very same order of succession. It is needless to multiply examples, or every part of the coast from Flamborough to Saltburn might be cited in proof of the

above important proposition. And though we only refer to a particular district, yet, without doubt, any part of the world, where the strata are distinctly visible, would equally illustrate the doctrine of local constancy in the order of succession among rocks; because in every country this conclusion has been drawn from actual observations. But it may be inquired: How can the strata be thus traced across provinces and kingdoms? we see them, indeed, exposed on the sea-coast, but how are we to guide our inquiries inland, when wells and pits fail us? I answer, that as the different rocks lie not quite horizontal, but gently sloping into the interior, the surface of the earth is formed on their edges. Thus, compare the accompanying geological map and section, and observe in the section the chalk rising uninterruptedly from Bridlington to Speeton, when, another stratum, the blue clay, having risen from beneath it to the surface,—that rock passes off inland, and keeps a regular course through the country. In the same manner, the calcareous grit rises from the sea at Filey, ascends to the summits of Gristhorpe and Red cliffs, afterwards attains the height of Oliver's mount, and ranges away in a direction parallel to the chalk. The same is the case with all the other strata, represented by the colours on the map. Thus, the surface of the earth is formed on the edges of the strata, a wise and admirable provision, whereby mankind, though till lately regardless of the benefit, are provided with so great a variety of mineral matter, suited to the various and increasing wants of civilized life. To trace the rocks through the interior of a country, demands, it must be confessed, greater diligence and caution, than when we see them exposed on the sea-side; but the result, thus prudently obtained, may be as absolutely trusted. Nor are facilities wanting to the practised inquirer. To him, the forms of hills, the character of surface, the very herbage and colour of the soil, afford most valuable data, and when corrected by the accounts of wells and pits, and observations of roads and water-courses, leave little room to doubt the accuracy of his deductions,

This being proved, we may now inquire if there be a conformity of rocks over large districts, an accordance of composition, a similarity of succession, and a connexion of strata, sufficient to unite together obser