their Relation to Geological Formations. 203 
with its most abundant calciec constituent. The same process, it 
may be urged, would take place over the shallower areas covered 
with foraminifer-ooze. Admitted, but with this difference : in 
the “red-clay’ basins foraminifer life evidently approaches 
zero, whereas in shallower areas it is unquestionably in the 
ascendant ; therefore any loss of lime the latter areas may 
sustain through the action of sulphurous acid, would be made 
up by dév’ng Foraminifera converting the sulphate of lime in 
the surrounding water into the carbonate composing their 
shells. 
Doubtless, whatever the agent may be that produces the 
‘red-clay”’ deposit, it has contributed more or less to the pro- 
duction of similar or related formations belonging to different 
geological periods—though they may be of any colour, depend- 
ing on the relative amount of their constituents and the nature 
of their combination. Certain supersilicated rocks (as nova- 
culite, fuller’s earth, chamoisite, &c.) suggest themselves in con- 
nexion with this idea; and it is highly probable that many of 
the glauconites were originally red clays (the residue of forami- 
nifer-ooze), part of the peroxide of iron of the latter having 
been reduced to a protoxide by organic matter. I cannot, 
however, think it is correct to associate the Oldhamian 
schists (Cambrian) with this idea—that is, “to suspect that 
they may be organic formations like the modern red clay 
of the Atlantic and Southern sea, accumulations of the in- 
soluble ashes of shelled creatures.” The thousands of feet 
of Cambrian schists would require the existence somewhere 
of vastly more thousands of feet of synchronous limestones. 
But where are they? In the recently published paper by 
Mr. Tl’. Davidson and myself on the Trimerellide this ques- 
tion was briefly discussed *. Failing to ascertain the existence 
of any limestones of the kind, we made the suggestion that 
the Cambrian seas were not inhabited by organisms furnished 
with calcareous skeletons, or they did not contain the ordi- 
nary amount of calcic constituents. I do not dispute that 
bicarbonate of lime carried into the sea by rivers, he naturally concluded 
that this salt was appropriated by shell-fish. Nevertheless I must still 
adhere to the opinion I expressed in 1862, that pelagic animals obtain 
calcic matter from the sulphate of lime contained in the surrounding 
water. I find that Forchhammer is of opinion ‘‘ that Testacea decompose 
the latter substance by means of carbonate of ammonia formed by their 
agency.” Bischof thinks that ‘it might likewise be decomposed by the 
organic matter of marine animals into sulphide of calcium, which would 
be decomposed by the carbonic acid produced by them”’ (see ‘Chemical 
Geology,’ vol. i. p. 180, footnote). 
* Quarterly Journal of the Geological Society, May 1874. 
