Life's Dawn on Earth: Being the history of the oldest known fossil remains, and their relations to geological time and to the development of the animal kingdomDawson, John William, Sir
History
Life's Dawn on Earth: Being the history of the oldest known fossil remains, and their relations to geological time and to the development of the animal kingdom
Dawson, John William, Sir
Life -- Origin; Paleontology -- Precambrian
It is different, however, with the round cells infiltrated with
serpentine and with the silicious grains included in the loganite. I
have already referred to and figured (fig. 18) the remarkable rounded
bodies occurring at Long Lake. I now figure similar bodies found mixed
with fragmental Eozoon and in separate thin layers at St. Pierre (fig.
32), also some of the singular grains found in the loganite occupying
the chambers of Eozoon from Burgess (fig. 33), and a beaded body set
free by acid, with others of irregular forms, from the limestone of
Wentworth (fig. 34). All these I think are essentially of the same
nature, namely, chambers originally invested with a tubulated wall
like Eozoon, and aggregated in groups, sometimes in a linear manner,
sometimes spirally, like those Globigerinæ which constitute the mass
of modern deep-sea dredgings and also of the chalk. These bodies occur
dispersed in the limestone, arranged in thin layers parallel to the
bedding or sometimes in the large chamber-cavities of Eozoon. They
are so variable in size and form that it is not unlikely they may be
of different origins. The most probable of these may be thus stated.
First, they may in some cases be the looser superficial parts of the
surface of Eozoon broken up into little groups of cells. Secondly,
they may be few-celled germs or buds given off from Eozoon. Thirdly,
they may be smaller Foraminifera, structurally allied to Eozoon, but
in habit of growth resembling those little globe-shaped forms which,
as already stated, abound in chalk and in the modern ocean. The latter
view I should regard as highly probable in the case of many of them;
and I have proposed for them, in consequence, and as a convenient name,
_Archæospherinæ_, or ancient spherical animals.
Carbonaceous matter is rare in the true Eozoon limestones, and, as
already stated, I would refer the Laurentian graphite or plumbago
mainly to plants. With regard to the worm-burrows referred to in 1865,
there can be no doubt of their nature, but there is some doubt as to
whether the beds that contain them are really Lower Laurentian. They
may be Upper Laurentian or Huronian. I give here figures of these
burrows as published in 1866[AG] (fig. 35). The rocks which contain
them hold also fragments of Eozoon, and are not known to contain other
fossils.
[Footnote AG: _Journal of Geological Society._]
[Illustration: Fig. 35. _Annelid Burrows, Laurentian or Huronian._
Fig 1. _Transverse section of Worm-burrow_--magnified, as a transparent
object. (_a._) Calcareo-silicious rock. (_b._) Space filled with
calcareous spar. (_c._) Sand agglutinated and stained black. (_d._)
Sand less agglutinated and uncoloured. Fig. 2. _Transverse section of
Worm-burrow on weathered surface_, natural size. Fig. 3. _The same_,
magnified.]
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