396 S. V. Wood—Origin of the Loess. 
deposit), during the short time, geologically speaking, since the 
commencement of the Glacial Period (for the remains said to occur 
in it would show this lmit in time), is so difficult of realization, 
that we may judiciously withhold all opinion about it until it has been 
examined more thoroughly than has hitherto been the case; but as 
regards the calcareous tubes with which it is said to be permeated, 
and which are regarded by the supporters of the dust theory as 
evidence of the roots of vegetation, growing on the surface which 
was continually under accretion from supplies of dust, it would be 
well if they, and all who regard small calcareous and ferruginous 
tubes destitute of carbonaceous. matter as indicative of roots, would 
weigh, and if possible clear up, the phenomena called by the late 
Charles Moore, in vol. xxxvii. of the Journ. of the Geol. Soc. pp. 71, 
79, and 81, Tubutella ambiqua, and found by him to occur in various 
formations (including modern brick-earths with freshwater shells) ; 
but which, though he thought they were of vegetable origin, occu- 
pied positions very difficult of reconciliation with it, as e.g. in the 
material filling deep fissures in the Carboniferous Limestone, and in 
what, to all appearance, was a mineral vein in the same limestone. 
These tubes he had submitted to friends, specially versed in various 
branches of science and natural history, with the result of obtaining 
from them the most conflicting opinions as to the organic or in- 
organic, animal or vegetable, origin of them. 
In conclusion, I take this opportunity of mentioning that though 
M. de Mercey, whose minute description of the Picardy loam I con- 
densed in first broaching my view of the origin of the Loess, speaks 
of this loam being formed of silex grains resulting from the con- 
tinuous rupturing of the Chalk flints, and as free from any admixture 
of carbonate of lime, yet as Prof. Prestwich, writing (in the Phil. 
Trans. for 1860) of the loam (or loess) with angular flint fragments 
which overlies the gravel of the Somme valley, describes it, in one 
instance as “ very,” and in another as “slightly ” calcareous, I take 
it that the escape of the water of the summer sludge laterally along 
the perennially frozen surface beneath did not altogether remove the 
calcareous matter by dissolution, leaving only the ruptured flint in 
grains of more or less minuteness, and in “ éclats,” behind, but that vary- 
ing quantities of the macerated chalk itself were left to intermingle 
with the material which there resulted, as Loess, from the disintegra- 
tion of tke flint. As calcareous formations furnish the most favour- 
able pabulum for the material described in my memoir, calcareous 
matter must often enter largely into the composition of that material. 
It occurred to me after my Newer Pliocene memoir was published, 
that the view I take of the intrusive cave earth with angular fragments 
being the material thus arising from the annual thaw of the upper 
surface only of the perennially frozen ground, sliding over the 
land during the minor glaciation, and finding its way into the caves 
through fissures in the rock above, was open to the objection that 
when the material had once penetrated a fissure to a depth corre- 
* These are said (by Todd and by Broadhead) to occur also in the American Loess, 
though (according to the former) restricted to the upper 30 or 40 feet. 
