THE NEW EDITION OF LYELL'S GEOLOGY.*

[SECOND NOTICE.]

IN our last notice we omitted the chapters on volcanic agency in Vol. I., stating that the subject would be noticed in connection with Mount Etna. The main object of whatever of new is in these chapters is the establishment of the argument against the -submarine origin of the Neapolitan and other Italian tufas. -Considerable addition have been made in this edition to the discussion of the structure of Mount Etna. They are stated to be the result of the re-examination of that volcano by -Sir C. Lyell in 1857 and 1858, and they consist partly of the establishment and explanation of the theory of a "double axis of eruption," a term perhaps easily misunderstood. That theory may be briefly explained thus. The ordinary form of volcanic mountains is generally observed to be a regularly shaped cone, the crater being at the summit and the strata sloping away from the -centre to all points of the compass, a position which has been called the " qutquiversal dip." But in Etna there appears to be an exception to this rule, some of the strata near the summit being nearly horizontal, with a steep slope downwards from the extremity of them furthest from the great crater. An analogous formation is said to be seen in some of the great Javanese volcanoes, where has is in one case specified) twin cones are joined by a saddle, on which the beds of lava or ashes are horizontal. Sir C. Lyell, • Principles of Geology; or, the Modern Changes of the Earth and its Inhabitants Con- sidered as Illustrative of Geology. By Sir Charles Lyell, Bart., MA., F.E.S. Tenth and entirely revised edition. 2 vols. London: Murray. 1887.

therefore, records the conclusion with regard to Etna that origin- ally there was a second crater in operation jointly with the great one which now exists, situated about six miles south-east of the present crater, but covered and obliterated since its extinction by the produce of the activity of the present crater. He also states that it is his opinion that the cone of Etna, as also that of Vesuvius, is the result of eruption rather than of upheaval.

An account is given of the eruption of 1866 in the gulf of Santorin, during and after which a new island, called Aphroessa, was raised, and attained an elevation of more than sixty feet where the soundings had been marked in the Admiralty chart as seventy fathoms. And in the following chapter on earthquakes and their effects the results of recent convulsions in New Zealand (1855) are described, and the origin and mode of propagation of earthquake waves are discussed. By a practical application of mechanical principles and by aid of mathematical formulae it has been calculated at what depth the shock of an earthquake origi- nated, and it has been observed that in a manner analogous to the undulations of light and sound the earthquake wave may be reflected or refracted, when it passes from one medium to another of different density.

The suggestions of Mr. T. Evans in a paper read to the Royal Society, 1866, on the subject of the change of axis of rotation of the earth's crust give rise to some remarks on the subject of central fluidity which will deserve the reader's special attention.

The following conclusion has been arrived at :—

" The doctrine, therefore, of the pristine fluidity of the interior of the earth, and the gradual solidification of its crust consequent on the loss of internal heat by radiation into space, is one of many scientific hypo- theses which has been adhered to after the props by which it was at first supported have given way one after the other. The astronomer may find good reasons for ascribing the earth's form to the original fluidity of the mass in times long antecedent to the first introduction of living beings into the planet ; but the geologist must be content to regard the earliest monuments which it is his task to interpret as belonging to a period when the crust had already acquired great solidity and thickness, probably as great as it now possesses, and when volcanic rocks not essentially differing from those now produced were formed from time to time, the intensity of volcanic heat being neither greater nor less than it is now."

The remarkable discovery of a connection between the periodical changes in the spots of the sun and variations in terrestrial mag- netism of which an account is given in connection with the subject of the sources of volcanic heat, seems to give hope of discovering the means by which the heat lost by conduction into space may be restored to the earth, and a cause for the local concentration of heat in particular parts of its exterior.

The remainder of the book (chaps. xxxiv. to xlix.) is devoted to the consideration of the changes of the organic world now in pro- gress, and treats, as has been said, mainly of the subject of the origin and subsequent fate of species.

In order to give an idea of the theory of the transmutation of species, a theory intimately bound up with that of progressive development above mentioned, it may be worth while to quote the following short statement of the question (which appeared in former editions, as in this) :—

" We know, said Lamarck, that individuals which are mere varieties of the same species would, if their pedigree could be traced back far enough, terminate in a single stock ; so, according to the same train of reasoning, the speeies of a genus, and even the genera of a great family, must have had a common point of departure. What, then, was the single stem from which so many varieties of form have ramified ? Were there many of these, or are we to refer the origin of the whole animate creation, as the Egyptian priests did that of the universe, to a single egg ?"

Now, the theory of progressive development receives, as it has been said, strong support from the geological evidence that plants and animals of more simple organization existed on the gloge before those of more compound structure, and the latter were successively formed at more modern periods. This gives a partial answer to the above quoted questions.

But some further hypothesis becomes indispensable, in order to explain why, after an indefinite lapse of ages, there are still so many beings of the simplest structure. Why have the majority of existing creatures remained stationary throughout this long succession of epochs, while others have made such prodigious advances? The key to this part of the difficulty is found in the

slow but unceasing co-operation of influential principles ; first, the tendency to progressive advancement in organization, accompanied by greater dignity in instinct intelligence, &c. ; secondly, the force of external circumstances, of variations in the physical condition of the earth or the mutual relations of plants and animals. It is plain that the sole operation of the first of these principles would result in a completely and most minutely graduated scale of organ-

ized beings, the transition being insensible from the simplest to the most compound structures. The operation of the other tends, it may almost be said solely, to the introduction into this scheme of all kinds of anomalies, varieties, and chasms. Against this theory has been brought the fact that 3,000 years ago the species of cats, dogs, bulls, &c., of which we have mummied instances from Egypt, were identical in form and habit, and may be seen in all climates to keep the same characteristics with those instances of these species with which we are now and here familiar. But Lamarck gave the answer which would be given now, that the lapse of thirty or forty centuries is utterly insignificant in the history of a species, and that the variation in all the important natural circumstances which is an essential condition for change of species according to the theory in question has not taken place with regard to the species alluded to, in the course of the last 3,000 years.

In connection with this subject our author here gives at length his own opinions on the extinction of species which he considers to be going on at about the rate of the coming-in of new ones, and it is shown that the annual birth and the annual death of one species in the world (no slight degree of change) might only result in the disappearance of one mammifer in 40,000 years in a region of the dimensions of Europe. Some further discussion is introduced which it is impossible here even to sketch, embodying the labours and conclusions of Wallace, Darwin, Dr. Hooker, and others, on the origin and nature of species, and on what is termed natural selection in the vegetable not less than in the animal kingdom ; it must suffice to say that the theory of natural selection is strongly confirmed by the facts collected and compared.

This discussion is carried on through two more chapters (xxxvi.

and xxxvii.), containing a great deal of new matter on many sub- jects, including the effects both on animal and vegetable species of domestication, cultivation, hybridization, and artificial selection, the general direction of the argument being that it tends to show that the limits within which these processes are possible and the laws according to which they will be carried on are capable of definition, and will reward investigation ; and in regard to the origin of species, that of the two rival theories of (1) special creation, and (2) creation by variation and natural selection, the latter is that which is most clearly borne out by the facts. The greater part of the following three chapters (xxxviii., xxxix., and xl.), on the geographical distribution of species, is contained in former editions, but in the thirty-eighth the six great provinces which are inhabited by distinct species are pointed out ; it is shown that there is a considerable coincidence in the range of species in the two grand divisions of the organic world, and, as in previous .editions, attention is drawn to the important geological fact that the influence of climate predominates over all the causes which limit the range of species in the mammalia. In the chapter (xli., which is completely new) on insular floras and faunas, considered with reference to the origin of species, it is shown that as a Tule the flora and fauna of islands are connected with those of the nearest mainland, though this rule is in some cases so far modified that the connection is only that of a species with its genus, certain species being peculiar to certain single islands. The greater part of our author's observations on this subject are

confined to the Atlantic islands of the Madeiras and Canaries, apparently instances of special geological interest. A very inter- esting map is given showing the depth of the ocean between the

eastern archipelagos of the North Atlantic and the mainland, and distinct evidence is produced of their volcanic origin and conse- quent original separation from the mainland. The following facts are alluded to and discussed. All indigenous mammalia are want- ing except bats. There is a total dearth of Batrachians (frogs, &c.). Almost all the birds in the Atlantic islands are absolutely identical in species with those of the nearest mainland. The insects . . . . unlike the birds, exhibit a large proportion of indigenous species and a great many genera peculiar to the Atlantic islands represented in each separate archipelago by distinct species.

In the case of plants the indication of relationship to the nearest continent is yet more circumstantial. And with regard to land- shells every island has its distinct species, and the whole fauna, differs almost entirely from that of every other archipelago, as well as from that of Europe and Africa. Of Madeira the following observation is, we think, very justly made

lg No human being is believed to have ever landed in Madeira until the year 1419. Madeira now supports a population of about 80,000 souls, and when we consider the great beauty and fertility of the esland, and that it has existed ever since the Miocene epoch, we are not 'merely called upon to explain the absence of inferior animals, but why, If we adopt the theory of special creation, no race of mankind was formed -expressly to inhabit such a paradise." „ On this subject it is observed in conclusion that,— " The extent to which the species of mammalia, bird; insect; land- shells, and plants (whether flowering or cryptogamous) agree with continental species, or the degree in which those of different archipe- lagos or of different islands of the same group agree with each other, has unmistakable relation to the known facilities enjoyed by each class of crossing the ocean. Such a relationship accords well with the theory of Variation and Natural Selection, but with no other hypothesis yet suggested for explaining the origin of species."

Our author has inserted nearly a whole chapter in this edition on the subject of the origin and geographical distribution of man, and of this subject, as of some previously mentioned and only cursorily treated of in this review, it must suffice to state in the barest man- ner the heads of the argument now for the first time fully intro- duced into this book. It is argued that man has had, like every species of animal, a single birthplace. It is considered probable that the formation of marked races proceeded at a faster rate when man first emerged from the primitive dwelling-place place than now though, perhaps, his mind might be more affected by circumstances than his bodily form. Attention is called to the fact that each of the more marked races of the human family is limited to some great zoological province. The multiple origin of man is, however, dis- cussed, as is also the question whether man has been degraded from a higher or has risen from a lower state of civilization. And this chapter concludes with some remarks on the Reign of Law, and the cri- ticisms therein contained on Darwin's theory of natural selection lead our author back to the main subject of the last ten chapters, viz., the origin of species, and thence to a slight disquisition on the present reluctance with which new truths are accepted. and the anxiety and unhappiness caused by the scientific revelation from day to day of facts and laws which have been affecting us from time out of mind as much as they ever will.

A few additions and alterations have been made to the six remaining chapters, but they are substantially the same as in previous editions, and it is hardly necessary to do more than men- tion those to which our author himself calls attention in the preface to the second volume, namely, some remarks on the sub- marine forest at Bournemouth, Hants, and Dr. Dawson's descrip- tion of another in the Bay of Fundy, and some account of the monuments of prehistoric man in Europe, together with scattered remarks on the antiquity or the modern date of man as derived from geological evidence.

Such is the result offered to the public by Sir C. Lyell in this tenth edition of the Principles of Geology, and there is, we think, distinct evidence of an increasing spirit of scientific earnestness and sincerity, the growth of which is proportionate with the growth of the field in which it is able to display itself, never shrinking from adopting such conclusions as are warranted by successive contributions of evidence, never ceasing in a most untiring and zealous endeavour to extend the limits of our know- ledge, and never going beyond the limits of exact and legitimate inference. Such a spirit will prepare us to find that "in time, as in space, the confines of the universe lie beyond the reach of mortal ken "; in such a spirit "we shall discover everywhere clear proofs of a creative intelligence, and of his foresight, wisdom, and power."