A Manual of Elementary Geology.

by Charles Lyell.

PREFACE.

In consequence of the rapid sale of the third edition of the "Manual," of which 2000 copies were printed in January last, a new edition has been called for in less than a twelvemonth. Even in this short interval some new facts of unusual importance in palaeontology have come to light, or have been verified for the first time. Instead of introducing these new discoveries into the body of the work, which would render them inaccessible to the purchasers of the former edition, I have given them in a postscript to this Preface (printed and sold separately), and have pointed out at the same time their bearing on certain questions of the highest theoretical interest.[v-A]

As on former occasions, I shall take this opportunity of stating that the "Manual" is not an epitome of the "Principles of Geology," nor intended as introductory to that work. So much confusion has arisen on this subject, that it is desirable to explain fully the different ground occupied by the two publications. The first five editions of the "Principles" comprised a 4th book, in which some account was given of systematic geology, and in which the princ.i.p.al rocks composing the earth's crust and their organic remains were described. In subsequent editions this book was omitted, it having been expanded, in 1838, into a separate treatise called the "Elements of Geology," first re-edited in 1842, and again recast and enlarged in 1851, and ent.i.tled "A Manual of Elementary Geology."

Although the subjects of both treatises relate to geology, as their t.i.tles imply, their scope is very different; the "Principles" containing a view of the _modern_ changes of the earth and its inhabitants, while the "Manual"

relates to the monuments of _ancient_ changes. In separating the one from the other, I have endeavoured to render each complete in itself, and independent; but if asked by a student which he should read first, I would recommend him to begin with the "Principles," as he may then proceed from the known to the unknown, and be provided beforehand with a key for interpreting the ancient phenomena, whether of the organic or inorganic world, by reference to changes now in progress.

Owing to the former incorporation of the two subjects in one work, and the supposed ident.i.ty of their subject matter, it may be useful to give here a brief abstract of the contents of the "Principles," for the sake of comparison.

_Abstract of the "Principles of Geology," Eighth Edition._

BOOK I.

1. Historical sketch of the early progress of geology, chaps. i. to iv.

2. Circ.u.mstances which combined to make the first cultivators of the science regard the former course of nature as different from the present, and the former changes of the earth's surface as the effects of agents different in kind and degree from those now acting, chap. v.

3. Whether the former variations in climate established by geology are explicable by reference to existing causes, chaps. vi. to viii.

4. Theory of the progressive development of organic life in former ages, and the introduction of man into the earth, chap. ix.

5. Supposed former intensity of aqueous and igneous causes considered, chaps. x. and xi.

6. How far the older rocks differ in texture from those now forming, chap. xii.

7. Supposed alternate periods of repose and disorder, chap. xiii.

BOOK II.

CHANGES NOW IN PROGRESS IN THE INORGANIC WORLD.

8. Aqueous causes now in action: Floods--Rivers--Carrying power of ice--Springs and their deposits--Deltas--Waste of cliffs and strata produced by marine currents: chaps. xiv. to xxii.

9. Permanent effects of igneous causes now in operation: Active volcanos and earthquakes--their effects and causes: chaps. xxiii. to x.x.xiii.

BOOK III.

CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS.

10. Doctrine of the trans.m.u.tation of species controverted, chaps. x.x.xiv. and x.x.xv.

11. Whether species have a real existence in nature, chaps. x.x.xvi. and x.x.xvii.

12. Laws which regulate the geographical distribution of species, chaps.

x.x.xviii. to xl.

13. Creation and extinction of species, chaps. xli. to xliv.

14. Imbedding of organic bodies, including the remains of man and his works, in strata now forming, chaps. xlv. to l.

15. Formation of coral reefs, chap. li.

It will be seen on comparing this a.n.a.lysis of the contents of the "Principles" with the headings of the chapters of the present work (see p.

xxiii.), that the two treatises have but little in common; or, to repeat what I have said in the Preface to the 8th edition of the "Principles,"

they have the same kind of connection which Chemistry bears to Natural Philosophy, each being subsidiary to the other, and yet admitting of being considered as different departments of science.[vi-A]

CHARLES LYELL.

_11 Harley Street, London, December 10. 1851._

FOOTNOTES:

[v-A] Postscript to 4th edition of the Manual, price 6_d._

[vi-A] As it is impossible to enable the reader to recognize rocks and minerals at sight by aid of verbal descriptions or figures, he will do well to obtain a well-arranged collection of specimens, such as may be procured from Mr. Tennant (149. Strand), teacher of Mineralogy at King's College, London.

POSTSCRIPT.

Tracks of a Lower Silurian reptile in Canada--Chelonian footprints in Old Red Sandstone, Morayshire--Skeleton of a reptile in the same formation in Scotland--Eggs of Batrachians (?) in a lower division of the "Old Red," or Devonian--Footprints of Lower Carboniferous reptiles in the United States--Fossil rain-marks of the Carboniferous period in Nova Scotia--Tria.s.sic Mammifer from the Keuper of Stuttgart--Cretaceous Gasteropoda--Dicotyledonous leaves in Lower Cretaceous strata--Bearing of the recent discoveries above-mentioned on the theory of the progressive development of animal life.

_Tracks of a Lower Silurian reptile in Canada._--In the year 1847, Mr.

Robert Abraham announced in the Montreal Gazette, of which he was editor, that the track of a freshwater tortoise had been observed on the surface of a stratum of sandstone in a quarry opened on the banks of the St. Lawrence at Beauharnais in Upper Canada. The inhabitants of the parish being perfectly familiar with the track of the amphibious mud-turtles or terrapins of their country, a.s.sured Mr. Abraham that the fossil impressions closely resembled those left by the recent species on sand or mud. Having satisfied himself of the truth of their report, he was struck with the novelty and geological interest of the phenomenon. Imagining the rock to be the lowest member of the old red sandstone, he was aware that no traces had as yet been found of a reptile in strata of such high antiquity.

He was soon informed by Mr. Logan, at that time engaged in the geological survey of Canada, that the white sandstone above Montreal was really much older than the "Old Red," or Devonian. It had in fact been ascertained many years before, by the State surveyors of New York (who called it the "Potsdam Sandstone"), to lie at the base of the whole Silurian series. As such it had been pointed out to me in 1841, in the valley of the Mohawk, by Mr. James Hall[vii-A], and its position was correctly described by Mr.

Emmons, on the borders of Lake Champlain, where I examined it in 1842. It has there the character of a shallow-water deposit, ripple-marked throughout a considerable thickness, and full of a species of Lingula. The flat valves of this sh.e.l.l, of a dark colour, are so numerous, and so arranged in horizontal layers, as to play the part of mica, causing the rock to divide into laminae, as in some micaceous sandstones.

When I mentioned this rock in my Travels[vii-B] as occurring between Kingston and Montreal, (the same in which the Chelonian foot-prints have since been found,) I spoke of it as the lowest member of the Lower Silurian series; but no traces of any organic being of a higher grade than the Lingula had then been seen in it, and I called attention to the singular fact, that the oldest fossil form then known in the world, was a marine sh.e.l.l strictly referable to a genus now existing.

Early in the year 1851, Mr. Logan laid before the Geological Society of London a slab of this sandstone from Beauharnais, containing no less than twenty-eight foot-prints of the fore and hind feet of a quadruped, and six casts in plaster of Paris, exhibiting a continuation of the same trail.

Each cast contained from twenty-six to twenty-eight impressions with a median channel equidistant from the two parallel rows of foot-prints, the one made by the feet of the right side, the other by those of the left. In these specimens a greater number of successive foot-marks belonging to one and the same series were displayed than had ever before been observed in any rock ancient or modern. Mr. Abraham has inferred that the breadth of the quadruped was from five to seven inches. A detailed account of the trail was published by Professor Owen, in April 1851, from which the following extracts are made.

"The foot-prints are in pairs, and the pairs extend in two parallel series, with a channel exactly midway between the right and left series. The pairs of the same side succeed each other at intervals, varying from one inch and a half to two inches and a half, the common distance being about two inches. The interval between the right and left pairs, measured from the inner border of the small prints, is three inches and a half, and from the outer border of the exterior or large prints, is seven inches. The shallow median track is one inch and a quarter in breadth, varying in depth, but not in its relative position to the right and left foot prints."

"The inference to be deduced from these characters is, that the impressions were made by a quadruped with the hind feet larger and somewhat wider apart than the fore feet, with both hind and fore feet either very short, or prevented by some other part of the animal's structure from making long steps; and with the limbs of the right side wide apart from those of the left; consequently, that the quadruped had a broad trunk in proportion to its length, supported on limbs either short, or capable only of short steps, and with rounded and stumpy feet, not provided with long claws.

There are faint traces of a fine reticulate pattern of the cuticle of the sole at the bottom of some of the foot-prints on one portion of the sandstone; and the surface of the sand is generally smoother there than where not impressed, which, with the rising of the sand at the border of the prints, indicates the weight of the impressing body. The median groove may be interpreted as due either to the abdomen or the tail of the animal; but as there is no indication of any bending or movement of a tail from side to side, it was probably scooped out of the soft sand by a hard breast-plate or plastron. If this were so, it may be inferred that the species was a freshwater or estuary tortoise rather than a land tortoise."[viii-A]