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Footnotes
Footnotes:
{1} 'Lecons de Geologie Pratique,' tom. i. 1845, p. 140.
{2} 'Transactions Geolog. Soc.' vol. v. p. 505. Read November 1,
1837.
{3} 'Histoire des progres de la Geologie,' tom. i. 1847, p. 224.
{4} 'Zeitschrift fur wissenschaft. Zoologie,' B. xxviii. 1877, p.
361.
{5} 'Gardeners' Chronicle,' April 17, 1869, p. 418.
{6} Mr. Darwin's attention was called by Professor Hensen to P. E.
Muller's work on Humus in 'Tidsskrift for Skovbrug,' Band iii. Heft
1 and 2, Copenhagen, 1878. He had, however, no opportunity of
consulting Muller's work. Dr. Muller published a second paper in
1884 in the same periodical--a Danish journal of forestry. His
results have also been published in German, in a volume entitled
'Studien uber die naturlichen Humusformen, unter deren Einwirkung
auf Vegetation und Boden,' 8vo., Berlin, 1887.
{7} 'Bidrag till Skandinaviens Oligochaetfauna,' 1871.
{8} 'Die bis jetzt bekannten Arten aus der Familie der
Regenwurmer,' 1845.
{9} There is even some reason to believe that pressure is actually
favourable to the growth of grasses, for Professor Buckman, who
made many observations on their growth in the experimental gardens
of the Royal Agricultural College, remarks ('Gardeners' Chronicle,'
1854, p. 619): "Another circumstance in the cultivation of grasses
in the separate form or small patches, is the impossibility of
rolling or treading them firmly, without which no pasture can
continue good."
{10} I shall have occasion often to refer to M. Perrier's
admirable memoir, 'Organisation des Lombriciens terrestres' in
'Archives de Zoolog. exper.' tom. iii. 1874, p. 372. C. F. Morren
('De Lumbrici terrestris Hist. Nat.' 1829, p. 14) found that worms
endured immersion for fifteen to twenty days in summer, but that in
winter they died when thus treated.
{11} Morren, 'De Lumbrici terrestris Hist. Nat.' &c., 1829, p. 67.
{12} 'De Lumbrici terrestris Hist. Nat.' &c., p. 14.
{13} Histolog. Untersuchungen uber die Regenwurmer. 'Zeitschrift
fur wissenschaft. Zoologie,' B. xix., 1869, p. 611.
{14} For instance, Mr. Bridgman and Mr. Newman ('The Zoologist,'
vol. vii. 1849, p. 2576), and some friends who observed worms for
me.
{15} 'Familie der Regenwurmer,' 1845, p. 18.
{16} 'The Zoologist,' vol. vii. 1849, p. 2576.
{17} 'Familie der Regenwurmer,' p. 13. Dr. Sturtevant states in
the 'New York Weekly Tribune' (May 19, 1880) that he kept three
worms in a pot, which was allowed to become extremely dry; and
these worms were found "all entwined together, forming a round mass
and in good condition."
{18} 'De Lumbrici terrestris Hist. Nat.' p. 19.
{19} 'Archives de Zoologie experimentale,' tom. vii. 1878, p. 394.
When I wrote the above passage, I was not aware that Krukenberg
('Untersuchungen a. d. physiol. Inst. d. Univ. Heidelberg,' Bd.
ii. p. 37, 1877) had previously investigated the digestive juice of
Lumbricus. He states that it contains a peptic, and diastatic, as
well as a tryptic ferment.
{20} On the action of the pancreatic ferment, see 'A Text-Book of
Physiology,' by Michael Foster, 2nd edit. pp. 198-203. 1878.
{21} Schmulewitsch, 'Action des Sucs digestifs sur la Cellulose.'
Bull. de l'Acad. Imp. de St. Petersbourg, tom. xxv. p. 549. 1879.
{22} Claparede doubts whether saliva is secreted by worms: see
'Zeitschrift fur wissenschaft. Zoologie,' B. xix. 1869, p. 601.
{23} Perrier, 'Archives de Zoolog. exper.' July, 1874, pp. 416,
419.
{24} 'Zeitschrift fur wissenschaft. Zoologie,' B. xix, 1869, pp.
603-606.
{25} De Vries, 'Landwirth. Jahrbucher,' 1881, p. 77.
{26} M. Foster, 'A Text-Book of Physiology,' 2nd edit. 1878, p.
243.
{27} M. Foster, ut sup. p. 200.
{28} Claparede remarks ('Zeitschrift fur wisseuschaft. Zoolog.'
B. 19, 1869, p. 602) that the pharynx appears from its structure to
be adapted for suction.
{29} An account of her observations is given in the 'Gardeners'
Chronicle,' March 28th, 1868, p. 324.
{30} London's 'Gard. Mag.' xvii. p. 216, as quoted in the
'Catalogue of the British Museum Worms,' 1865, p. 327.
{31} 'Familie der Regenwurmer,' p. 19.
{32} In these narrow triangles the apical angle is 9 degrees 34
seconds, and the basal angles 85 degrees 13 seconds. In the
broader triangles the apical angle is 19 degrees 10 seconds and the
basal angles 80 degrees 25 seconds.
{33} See his interesting work, 'Souvenirs entomologiques,' 1879,
pp. 168-177.
{34} Mobius, 'Die Bewegungen der Thiere,' &c., 1873, p. 111.
{35} 'Annals and Mag. of N. History,' series ii. vol. ix. 1852, p.
333.
{36} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 405.
{37} I state this on the authority of Semper, 'Reisen im Archipel
der Philippinen,' Th. ii. 1877, p. 30.
{38} Dr. King gave me some worms collected near Nice, which, as he
believes, had constructed these castings. They were sent to M.
Perrier, who with great kindness examined and named them for me:
they consisted of Perichaeta affinis, a native of Cochin China and
of the Philippines; P. Luzonica, a native of Luzon in the
Philippines; and P. Houlleti, which lives near Calcutta. M.
Perrier informs me that species of Perichaeta have been naturalized
in the gardens near Montpellier and in Algiers. Before I had any
reason to suspect that the tower-like castings from Nice had been
formed by worms not endemic in the country, I was greatly surprised
to see how closely they resembled castings sent to me from near
Calcutta, where it is known that species of Perichaeta abound.
{39} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p.
364.
{40} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p.
356.
{41} Perrier, 'Archives de Zoolog. exper.' tom. 3, p. 378, 1874.
{42} This case is given in a postscript to my paper in the
'Transact. Geolog. Soc.' (Vol. v. p. 505), and contains a serious
error, as in the account received I mistook the figure 30 for 80.
The tenant, moreover, formerly said that he had marled the field
thirty years before, but was now positive that this was done in
1809, that is twenty-eight years before the first examination of
the field by my friend. The error, as far as the figure 80 is
concerned, was corrected in an article by me, in the 'Gardeners'
Chronicle,' 1844, p. 218.
{43} These pits or pipes are still in process of formation.
During the last forty years I have seen or heard of five cases, in
which a circular space, several feet in diameter, suddenly fell in,
leaving on the field an open hole with perpendicular sides, some
feet in depth. This occurred in one of my own fields, whilst it
was being rolled, and the hinder quarters of the shaft horse fell
in; two or three cart-loads of rubbish were required to fill up the
hole. The subsidence occurred where there was a broad depression,
as if the surface had fallen in at several former periods. I heard
of a hole which must have been suddenly formed at the bottom of a
small shallow pool, where sheep had been washed during many years,
and into which a man thus occupied fell to his great terror. The
rain-water over this whole district sinks perpendicularly into the
ground, but the chalk is more porous in certain places than in
others. Thus the drainage from the overlying clay is directed to
certain points, where a greater amount of calcareous matter is
dissolved than elsewhere. Even narrow open channels are sometimes
formed in the solid chalk. As the chalk is slowly dissolved over
the whole country, but more in some parts than in others, the
undissolved residue--that is the overlying mass of red clay with
flints,--likewise sinks slowly down, and tends to fill up the pipes
or cavities. But the upper part of the red clay holds together,
aided probably by the roots of plants, for a longer time than the
lower parts, and thus forms a roof, which sooner or later falls in,
as in the above mentioned five cases. The downward movement of the
clay may be compared with that of a glacier, but is incomparably
slower; and this movement accounts for a singular fact, namely,
that the much elongated flints which are embedded in the chalk in a
nearly horizontal position, are commonly found standing nearly or
quite upright in the red clay. This fact is so common that the
workmen assured me that this was their natural position. I roughly
measured one which stood vertically, and it was of the same length
and of the same relative thickness as one of my arms. These
elongated flints must get placed in their upright position, on the
same principle that a trunk of a tree left on a glacier assumes a
position parallel to the line of motion. The flints in the clay
which form almost half its bulk, are very often broken, though not
rolled or abraded; and this may he accounted for by their mutual
pressure, whilst the whole mass is subsiding. I may add that the
chalk here appears to have been originally covered in parts by a
thin bed of fine sand with some perfectly rounded flint pebbles,
probably of Tertiary age; for such sand often partly fills up the
deeper pits or cavities in the chalk.
{44} S. W. Johnson, 'How Crops Feed,' 1870, p. 139.
{45} 'Nature,' November 1877, p. 28.
{46} 'Proc. Phil. Soc.' of Manchester, 1877, p. 247.
{47} 'Trans. of the New Zealand Institute,' vol. xii., 1880, p.
152.
{48} Mr. Lindsay Carnagie, in a letter (June 1838) to Sir C.
Lyell, remarks that Scotch farmers are afraid of putting lime on
ploughed land until just before it is laid down for pasture, from a
belief that it has some tendency to sink. He adds: "Some years
since, in autumn, I laid lime on an oat-stubble and ploughed it
down; thus bringing it into immediate contact with the dead
vegetable matter, and securing its thorough mixture through the
means of all the subsequent operations of fallow. In consequence
of the above prejudice, I was considered to have committed a great
fault; but the result was eminently successful, and the practice
was partially followed. By means of Mr. Darwin's observations, I
think the prejudice will be removed."
{49} This conclusion, which, as we shall immediately see, is fully
justified, is of some little importance, as the so-called bench-
stones, which surveyors fix in the ground as a record of their
levels, may in time become false standards. My son Horace intends
at some future period to ascertain how far this has occurred.
{50} Mr. R. Mallet remarks ('Quarterly Journal of Geolog. Soc.'
vol. xxxiii., 1877, p. 745) that "the extent to which the ground
beneath the foundations of ponderous architectural structures, such
as cathedral towers, has been known to become compressed, is as
remarkable as it is instructive and curious. The amount of
depression in some cases may be measured by feet." He instances
the Tower of Pisa, but adds that it was founded on "dense clay."
{51} 'Zeitschrift fur wissensch. Zoolog.' Bd. xxviii., 1877, p.
360.
{52} See Mr. Dancer's paper in 'Proc. Phil. Soc. of Manchester,'
1877, p. 248.
{53} 'Lecons de Geologie pratique,' 1845, p. 142.
{54} A short account of this discovery was published in 'The
Times' of January 2, 1878; and a fuller account in 'The Builder,'
January 5, 1878.
{55} Several accounts of these ruins have been published; the best
is by Mr. James Farrer in 'Proc. Soc. of Antiquaries of Scotland,'
vol. vi., Part II., 1867, p. 278. Also J. W. Grover, 'Journal of
the British Arch. Assoc.' June 1866. Professor Buckman has
likewise published a pamphlet, 'Notes on the Roman Villa at
Chedworth,' 2nd edit. 1873 Cirencester.
{56} These details are taken from the 'Penny Cyclopaedia,' article
Hampshire.
{57} "On the denudation of South Wales," &c., 'Memoirs of the
Geological Survey of Great Britain,' vol. 1., p. 297, 1846.
{58} 'Geological Magazine,' October and November, 1867, vol. iv.
pp. 447 and 483. Copious references on the subject are given in
this remarkable memoir.
{59} A. Tylor "On changes of the sea-level," &c., ' Philosophical
Mag.' (Ser. 4th) vol. v., 1853, p. 258. Archibald Geikie,
Transactions Geolog. Soc. of Glasgow, vol. iii., p. 153 (read
March, 1868). Croll "On Geological Time," 'Philosophical Mag.,'
May, August, and November, 1868. See also Croll, 'Climate and
Time,' 1875, Chap. XX. For some recent information on the amount
of sediment brought down by rivers, see 'Nature,' Sept. 23rd,
1880. Mr. T. Mellard Reade has published some interesting articles
on the astonishing amount of matter brought down in solution by
rivers. See Address, Geolog. Soc., Liverpool, 1876-77.
{60} "An account of the fine dust which often falls on Vessels in
the Atlantic Ocean," Proc. Geolog. Soc. of London, June 4th, 1845.
{61} For La Plata, see my 'Journal of Researches,' during the
voyage of the Beagle, 1845, p. 133. Elie de Beaumont has given
('Lecons de Geolog. pratique,' tom. I. 1845, p. 183) an excellent
account of the enormous quantity of dust which is transported in
some countries. I cannot but think that Mr. Proctor has somewhat
exaggerated ('Pleasant Ways in Science,' 1879, p. 379) the agency
of dust in a humid country like Great Britain. James Geikie has
given ('Prehistoric Europe,' 1880, p. 165) a full abstract of
Richthofen's views, which, however, he disputes.
{62} These statements are taken from Hensen in 'Zeitschrift fur
wissenschaft. Zoologie.' Bd. xxviii., 1877, p. 360. Those with
respect to peat are taken from Mr. A. A. Julien in 'Proc. American
Assoc. Science,' 1879, p. 354.
{63} I have given some facts on the climate necessary or
favourable for the formation of peat, in my 'Journal of
Researches,' 1845, p. 287.
{64} A. A. Julien "On the Geological action of the Humus-acids,"
'Proc. American Assoc. Science,' vol. xxviii., 1879, p. 311. Also
on "Chemical erosion on Mountain Summits;" 'New York Academy of
Sciences,' Oct. 14, 1878, as quoted in the 'American Naturalist.'
See also, on this subject, S. W. Johnson, 'How Crops Feed,' 1870,
p. 138.
{65} See, for references on this subject, S. W. Johnson, 'How
Crops Feed,' 1870, p. 326.
{66} This statement is taken from Mr. Julien, 'Proc. American
Assoc. Science,' vol. xxviii., 1879, p. 330.
{67} The preservative power of a layer of mould and turf is often
shown by the perfect state of the glacial scratches on rocks when
first uncovered. Mr. J. Geikie maintains, in his last very
interesting work ('Prehistoric Europe,' 1881), that the more
perfect scratches are probably due to the last access of cold and
increase of ice, during the long-continued, intermittent glacial
period.
{68} Many geologists have felt much surprise at the complete
disappearance of flints over wide and nearly level areas, from
which the chalk has been removed by subaerial denudation. But the
surface of every flint is coated by an opaque modified layer, which
will just yield to a steel point, whilst the freshly fractured,
translucent surface will not thus yield. The removal by
atmospheric agencies of the outer modified surfaces of freely
exposed flints, though no doubt excessively slow, together with the
modification travelling inwards, will, as may be suspected,
ultimately lead to their complete disintegration, notwithstanding
that they appear to be so extremely durable.
{69} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 409.
{70} 'Nouvelles Archives du Museum,' tom. viii. 1872, pp. 95,
131.
{71} Morren, in speaking of the earth in the alimentary canals of
worms, says, "praesepe cum lapillis commixtam vidi:" 'De Lumbrici
terrestris Hist. Nat.' &c., 1829, p. 16.
{72} Perrier, 'Archives de Zoolog. exper.' tom. iii. 1874, p. 419.
{73} Morren, 'De Lumbrici terrestris Hist. Nat.' &c., p. 16.
{74} 'Archives de Zoolog. exper.' tom. iii. 1874, p. 418.
{75} This conclusion reminds me of the vast amount of extremely
fine chalky mud which is found within the lagoons of many atolls,
where the sea is tranquil and waves cannot triturate the blocks of
coral. This mud must, as I believe ('The Structure and
Distribution of Coral-Reefs,' 2nd edit. 1874, p. 19), be attributed
to the innumerable annelids and other animals which burrow into the
dead coral, and to the fishes, Holothurians, &c., which browse on
the living corals.
{76} Anniversary Address: 'The Quarterly Journal of the
Geological Soc.' May 1880, p. 59.
{77} Mr. James Wallace has pointed out that it is necessary to
take into consideration the possibility of burrows being made at
right angles to the surface instead of vertically down, in which
case the lateral displacement of the soil would be increased.
{78} 'Elements of Geology,' 1865, p. 20.
{79} 'Lecons de Geologie pratique, 1845; cinquieme Lecon. All
Elie de Beaumont's arguments are admirably controverted by Prof. A.
Geikie in his essay in Transact. Geolog. Soc. of Glasgow, vol. iii.
p. 153, 1868.
{80} 'Illustrations of the Huttonian Theory of the Earth,' p. 107.
{81} Mr. E. Tylor in his Presidential address ('Journal of the
Anthropological Institute,' May 1880, p. 451) remarks: "It appears
from several papers of the Berlin Society as to the German 'high-
fields' or 'heathen-fields' (Hochacker, and Heidenacker) that they
correspond much in their situation on hills and wastes with the
'elf-furrows' of Scotland, which popular mythology accounts for by
the story of the fields having been put under a Papal interdict, so
that people took to cultivating the hills. There seems reason to
suppose that, like the tilled plots in the Swedish forest which
tradition ascribes to the old 'hackers,' the German heathen-fields
represent tillage by an ancient and barbaric population."
{82} White of Selborne has some good remarks on the service
performed by worms in loosening, &c., the soil. Edit, by L.
Jenyns, 1843, p. 281.
{83} 'Zeitschrift fur wissenschaft. Zoolog.' B. xxviii. 1877, p.
360.
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