The doctrine of the central igneous fluidity of the earth is generally accepted by geologists. The hypothesis of intense chemical action as the cause of existing internal heat-a hypothesis first enunciated by Sir Humphry Davy*-is, however, revived from time to time under some novel modification. Dr. T. S. Hunt, while admitting the primordial incandescence of our planet, has maintained, in a series of lectures before the Lowell Institute of Boston, that the solid crust is probably not less than 2000 miles in thickness, and envelops a solid nucleus, with a comparatively thin belt of material between the two, which has been reduced to a soft and pasty condition by the combined action of heat, water, and chemical affinity. In his lecture on "Primeval Chemistry," more recently delivered before the American Institute in New York, he is reported as saying that "the earth must have a crust several hundred miles in thickness;" that "granite is in all cases a secondary rock, derived from sediments crystallized through the agency of water and heat;" and that "the theory which ascribes volcanic products to the supposed uncooled liquid centre fails entirely to account for the great diversity in composition of these products, all of which, wherever found, are represented in rocks of aqueous origin.'

Mr. N. S. Shaler has attempted to show, in an ingenious paper read before the Boston Society of Natural History (Proceedings, vol. xi., p. 8), that the solidification of the earth began at the centre and proceeded toward the periphery—that finally solidification began at the periphery and proceeded toward the centre, leaving, within the era of recognizable geological events, but an insignificant portion of the earth in its primordial fluid

state.

* Unless, indeed, Milton can be said to have first suggested it in the following words:

"The force

Of subterranean wind transports a hill
Torn from Pelorus, or the shattered side
Of thundering Etna, whose combustible
And fueled entrails thence conceiving fire,
Sublimed with mineral fury, aid the winds,
And leave a singed bottom all involved
With stench and smoke."-Paradise Lost, i., 230.

T

Professor James Hall, also, in his recent lecture before the American Institute on the "Evolution of the American Continent," is reported (in the New York Tribune) as advancing views which indicate that he has relapsed into the ranks of the most radical Neptunists. "I desire,” says he, to impress upon you this one truth, that we have not, in our geological investigation, succeeded in going back one step beyond the existence of water and stratification-one step toward this so-called primary nucleus of molten matter. So far as we have any knowledge of the materials in the interior of the globe, they appear to us only as trap dikes, and these occupying only a very small area upon the surface. This original nucleus that has been talked about in geology has produced no effect upon the surface of the earth; neither upon its mountain chains or any other of the great features of the continent.

“This idea of a great primary nucleus is only theoretical. It has not in it any thing tangible. The earliest rocks of which we have any knowledge were deposited by the ocean, under conditions similar to those which now exist. The conditions of the ocean currents are the same now as they have been from the earliest time. From the earliest history of the American continent-from the earliest history of any other, we know that the ocean currents have prevailed as they now prevail, moving northward. and southward; and here, at least, the transporting power has generally been from the north toward the south and west; and we have abundant evidence that all the materials composing our continent have been derived in that way from the transporting agency of currents of water alone."

Professor Hall seems to have taken the laurels from the brow of M. Comte in his resignation to the consequences of the Positive Philosophy. There are many positions in the foregoing quotation which are destined to be shaken as by an earthquake shock generated by those very internal fires which he so irreverently ignores. Though this is not the place for argument, I will not refrain from reminding the reader that if our world has been cooling for many ages, as science demonstrates that it is cooling to-day, there must have been a time when the first aqueous sediments accumulated. What was their origin? I very well understand that the reply will be, that we neither know that the earth has been in process of cooling from a high antiquity, nor have we seen, except in isolated patches, the supposed foundation-lavas and granites which constituted the primordial crust. When I stand by the Michigan Central Railway, and see the "Blue Line" freight-cars pass, bearing the inscription "Great Central Route; through freight from New York to the Mississippi," I should consider it folly to deny that these cars have proceeded from New York, and base my denial on the fact that I had never seen them at that point. It is thus that events rush past us, and he who will read the legends which they bear may learn somewhat both of the beginning and the end. Lack of demonstration is not necessarily nescience. It is too much the fashion of a certain school to apply the shears of nescience to scientific and philo

sophic systems, to crop and prune them to predetermined shapes. Whither the known points us, let us follow; and if we can not discern things clearly, let us be content to see them "through a glass darkly." It would be stupidity to ignore the existence of a solar orb even in total eclipse.

66

This revulsion in the popular view has to some extent been produced by the weight of well-known names recorded against the doctrine of primordial fusion and continued central fluidity. Sir David Brewster denounces "the nebulous theory" as utter nonsense;" and Mr. Evan Hopkins has publicly denied the accepted doctrine of a slow increase of temperature in penetrating toward the earth's centre. It is certain, however, that the facts upon which his denial rests have been generated by abnormal and perturbating influences. Mr. W. Hopkins several years since contended that the solidification of the earth must have begun at the centre, simultaneously with the formation of the superficial crust. Sir Wm. Thompson maintains that the rigidity of the earth is required by the phenomena of precession and nutation. Against these conclusions, however, Delauny very recently opposes the results of experiments which show that a body of water inclosed in a rotating glass globe promptly partakes of the rotation of the globe, and becomes physically a part of it. The author remains decidedly of the opinion that the balance of evidence sustains the doctrine of central fluidity. The reader who desires to examine farther the objections urged against this doctrine may consult Hopkins (Wm.), in Phil. Trans. of the Royal Society, 1836, p. 382; also 1839-40-42; also Quar. Jour. Geolog. Soc., Lond., vol. viii., p. 56; Thompson (W.), on the Rigidity of the Earth, in Proceedings Roy. Soc., vol. xii., p. 103; Tyndall, in Fortnightly Review. On the subject of mountain-formation, see Hall (James), Paleontology of New York, vol. iv., Introduction; Dana (J.D.), Address before the Amer. Assoc. for the Advancement of Science, Providence, 1857.

NOTE II., page 71.

As the recent discovery of traces of animal life two whole systems lower in the series of strata than had heretofore been known is an event of extraordinary importance in the progress of our knowledge of the world's preadamic history-insomuch that Sir Charles Lyell characterizes it as the greatest geological discovery of his time-I introduce here a somewhat complete series of references to the papers which have been published on the subject:

1858, May. Hunt (Dr. T. S.), Remarks on the presence of iron ores and graphite in Laurentian strata as affording evidence of the "existence of organic life even during the Laurentian or Azoic period.” Amer. Jour. Sci. and Arts [2], xxv., 436.

1858, Oct. Logan (Sir W. E.) received the first specimens of suspected

fossilferous rock from the Grand Calumet on the River Ottawa, collected by Mr. J. McMullen. Figured in “Geol. of Canada,” p. 49, and in numerous places since.

1859, Jan. Hunt (Dr. T. S.), Reiterates his convictions as to the "existence of an abundant vegetation during the Laurentian period.'

Quar. Jour. Geol. Soc., Lond. Reviewed Amer. Jour. [2], xxxi., 134.

1859, Aug. Logan (Sir W. E.), Exhibits specimens before Amer. Assoc. Adv. Sci. at Springfield.

1859. Logan (Sir W. E.), Publishes notice of the above. Canadian Naturalist, iv., 300.

1861, May. Hunt (Dr. T. S.), Sets forth more fully his views on probable Laurentian life. Amer. Jour. Sci. [2], xxxi., 396.

1862. Logan (Sir W. E.), Exhibits specimens in Great Britain which are held by Ramsay to be organic.

1862, Dec. Dana (Prof. J. D.), Suggests indications of organic life in Azoic rocks. Manual of Geology, p. 145.

1863. Logan (Sir W. E.), Describes and figures specimens from Grand Calumet. Geology of Canada, p. 49.

1864, Mar. Logan (Sir W. E.), Preliminary notice of additional specimens discovered by James Lowe in Grenville. Amer. Jour. [2], xxxvii.,

272.

1864, May. Hunt (Dr. T. S.), Preliminary notice of some specimens. Amer. Jour., xxxvii., 431.

1864, Nov. Sanford (Mr.), Announces Eozoön in Connemara marble of the Binabola Mountains, Ireland. Geological Magazine. Reannounced in "Reader," Feb. 25, 1865.

1865, Feb. The Quar. Jour. Geol. Soc., Lond., contains the following papers:

Logan (Sir W. E.), "On the occurrence of Organic Remains in the Laurentian Rocks of Canada.'

Dawson (Dr. J. W.), "On certain Organic Remains in the Laurentian Limestones of Canada." A microscopical investigation and determination of zoological relations.

Carpenter (Dr. W. B.), "Notes on the Structure and Affinities of Eozoön Canadense. Farther microscopical descriptions. Hunt (Dr. T. S.), "On the Mineralogy of Eozoön Canadense. The foregoing papers were republished in the Canadian Naturalist [2], ii., 92, April, 1865; also in a pamphlet entitled "On the History of Eozoön Canadense," April, 1865; also, with remarks by the editors, in Am. Jour. Sci. and Arts [2], xl., 344, Nov., 1865.

1865, April. Jones (Prof. T. R.), Discusses the geological and zoological relations of Eozoön. Popular Science Review.

1865, May. Carpenter (Dr. W. B.), Further discusses Eozoön. Intellectual Observer (two plates).

1865, June 10. King and Rowney (Profs.), Question the organic nature of Eozoön, while Dr. Carpenter sustains it, supported by the authority of Milne-Edwards.

1866, Feb. 10. Carpenter (Dr. W. B.), Announces Eozoön from Australia and Bavaria, and controverts the position of Profs. King and Rowney. Noticed in Amer. Jour. Sci. [2], xli., 406. 1866, Aug. King and Rowney (Profs.), "On the so-called Eozoönal rock, denying its organic character. Quar. Jour. Geol. Soc., Lond., xxii., pt. ii., 23. Their position is controverted in the same No. Their 'Summary" is reproduced Amer. Jour. Sci. [2], xliv., 375. 1866. Gümbel (Dr.), "Occurrence of Eozoön in East Bavarian primitive rocks." Sitzungsberichte d. K. Acad. d. W. in München, i., 1. Reproduced Quar. Jour. Geol. Soc., Lond., xxii., pt. i., p. 185. Noticed Amer. Jour. Sci. [2], xliii., 398. Confirmed by Carpenter, Proc. Roy. Soc., No. xciii., p. 508.

1867, May. Dawson and Logan. Describe new specimens of Eozoön from Tudor, C. W. Quar. Jour. Geol. Soc.

1867. Carpenter (Dr. W. B.), Reasserts organic nature of Eozoön in op

position to King and Rowney. Proc. Royal Soc., No. xciii., p. 503. 1867. Pusirevski (Prof.), Reports Eozoön Canadense at Hopinwara, Finland. Bull. Acad. St. Petersburg, x., 151. Noticed Amer. Jour. Sci. [2], xliv., 284.

1867, Nov. Dawson (J. W.), Notes on Eozoön from Tudor, C. W., from Long Lake and Wentworth, and from Madoc, with remarks by Dr. W. B. Carpenter. Amer. Jour. Sci. [2], xliv., 367. Republished Amer. Jour. Sci. [2], xlvi., 245 (Sept., 1868).

NOTE III., page 76.

As the reader may frequently desire to refresh his memory in reference to the order of superposition of the great groups of strata, the following table is appended for reference. The groups follow each other in the natural order of superposition.

CLASSIFICATION OF THE STRATIFIED ROCKS OF NORTH AMERICA.