APPENDIX.                                                537

B.— Chemical Analyses showing the absence of Phosphoric Acid in the
BocJcs below the Silurian Deposits (p. 28).

Ln order to ascertain indirectly the presence of phosphoric acid in rocks, my
valued friend Dr. Daubeny experimented upon the relative amount of produce
obtained from barley sown in pulverized samples of various strata of different
geological epochs. He found that, whatever the age of the rock might be,
provided it belonged to a series in whicb organic remains were present,
the amoimt of pbosphoric acid present in the crop exceeded considerably that
existing in the barley from wbicb it was derived, indicating that the above
material must have been one of the constituents of the rock, as this alone could
have supplied it to the plants growing in it. On the other hand, in certain slates
which lie below tbe oldest rocks in which many organic remains have been de¬
tected (such, for instance, as those of Nant Erancon, Llanberis near Bangor, and
to the north of Dolgelly, or schist taken from the foot of Skiddaw, and a sample
of mica-schist from Loch Lomond), the quantity of phosphoric acid present in tbe
crop barely exceeded that existing in the barley sown, indicating the almost
entire absence of this substance in the rock itself, and consequently leading us
to infer that very few organic remains could ever have existed in it, rather than
that the traces of them had been obliterated by subsequent metamorphic action,
inasmuch as we have no reason to suppose that any heat which might have
affected the strata would have dissipated the phosphoric acid contained in them,
many of the fossiliferous Silurian rocks containing phosphoric acid being equally
slaty.   (See Quarterly Journal of the Chemical Society of London, vol. vii.)

In subsequent researches Dr. Daubeny could detect no trace of phosphoric
acid in certain specimens from the Longmynd (which fundamental rock of the
Silurian region is no more altered than the overlying Silurian strata), whilst the
Ludlow rocks contained as much of it as any of the younger fossiliferous rocks
on which he experimented.

The determinations of the Chemist are thus in perfect harmony with the con¬
clusions of the Geologist and Palaeontologist, in establishing a decrement of life
as we descend through the strata forming the crust of the globe.

C.—Igneous Bocks of the Silurian Region of Britain compared ivith their
German equivalents (pp. 49 & 76).

In varioLis parts of this volume, but particularly in the Fourth Chapter, the .
rocks of igneous origin, whether cotemporaneous with or posterior to the strata
with which they are associated, are mentioned in terms of which German geo-
loo-ists must wish to know the exact import. My illustrious friend the late Baron
Humboldt, who requested me to send to him a few specimens of the character¬
istic Silurian types of this class of rocks, has spoken of them in his fourth
volume of ' Cosmos,' and also transmitted to me the following description of
them as furnished by his eminent associate. Prof Gustav Eose:—

" In accordance vsdth your wish, I send you herewith some remarks on the
rock-specimens forwarded by Sir R. Murchison. The rock-specimens termed
^greenstone,' from Pembroke, Caernarvonshu-e, and Anglesea, are different va¬
rieties of hypersthenite and gabbro, such as occur near Nem-ode in Silesia, or at
the Baste in the Harz—compounds of hypersthene or diaUage with labradorite,
which last has become snow-white or greenish white, and then is in the
incipient state of change to serpentine; the hypersthene and diallage are also

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