49 
and of tetractinellids form an important proportion of the whole 
rock. In addition, gasteropods, cephalopods, lamellibranchs, and 
echinoids are found, but unfortunately they are, as a rule, too 
poorly preserved for specific determination, though an extensive 
collection might ena1)le the s])ecies of some forms to be ascertained. 
Lithologically these beds are characterised by — 
(1) Their uniformly fine grain. 
(2) The comparatively small proportion of kaolin present. 
(b) The almost total absence of calcium or magnesium car- 
bonates. 
(4) The large ])roportion of purely siliceou^material present 
( quartz and oi)al ) . 
(a) The fact that siliceous foi)al) sponge spicules form an 
appreciable, at times a preponderating, part of the whole mass. 
(tj) The usual slight coherence of the ])articles to one another. 
d'he following arc analysesj of two coherent sandstones belong- 
ing to this series from Cape Riche : — 
While Stone. 
Vellow Stone. 
S1O2 sol. in 5 % 
Si02 insol. „ 
NaOH 
5, ... ... 
60 22 
^3-40 
cc 
cc 
AI2O3 
... ... 
6.2^ 
5 95 
FejOj 
... ... 
T -95 
234 
MgO 
... ... ... 
57 
■39 
CaO 
• • • . • . ... 
■'3 
nil 
H 2 0 above 100° 
2 74 
2-82 
H 2 0 ;it loo'^ 
. . ... ... 
3*50 
3'19 
Alkalis end loss 
... 
1-24 
2-43 
[OO'OO 
I OO'OO 
Bulk specific gravity 
133 
1-44 
'True specific gravity 
2 . I 8 
2 -20 
In consequence of having been laid down upon a very irregular 
surface of granite the thickness of the Plantagcnet Beds must be 
variable, in some places l)eing very thin and probably nowhere 
exceediu-g feet. Their exact age is tindelermined, but from 
the freciuently unconsolidated nature of the materials, their a])proxi- 
mately horizontal stratification, and the modern appearance of the 
contained fauna, the sediments cannot be very ancient. I'ossils 
from various localities have at times been examined by Mr. 
J Hy E.S.?. 
