APPENDIX. 
537 
B. — Chemical Analyses showing the absence of Phosphoric Acid in the 
Rocks below the Silurian Deposits (p. 28). 
In order to ascertain indirectly the presence of phosphoric acid in rocks, my 
valued friend Dr. Dauheny 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 which organic remains were present, 
the amount of phosphoric acid present in the crop exceeded considerably that 
existing in the barley from which 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 the oldest rocks in which many organic remains have been de- 
tected (such, for instance, as those of Nant Francon, 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 the 
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 Rocks of the Silurian Region of Britain compared with their 
German equivalents (pp. 49 & 76). 
In various 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- 
logists 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 1 Cosmos,' and also transmitted to me the following description of 
them as furnished by his eminent associate, Prof. Gustav Rose : — 
" In accordance with your wish, I send you herewith some remarks on the 
rock-specimens forwarded by Sir R. Murchison. The rock-specimens termed 
' greenstone,' from Pembroke, Caernarvonshire, and Anglesea, are different va- 
rieties of hypersthenite and gabbro, such as occur near Neurode in Silesia, or at 
the Baste in the Harz — compounds of hypersthene or diallage 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 
2n 
