336 
SECONDARY FORMATIONS. 
[Ch. XXIII. 
submarine eruptions ; but at some points, as in the Hebrides, 
it seems that the same ocean was the theatre of volcanic action. 
We have mentioned in the first volume *, that as the ancient 
eruptions occurred in succession, sufficient time usually inter- 
vening between them to allow of the accumulation of many- 
subaqueous strata, so also should we infer that subterranean 
movements, which are another portion of the volcanic pheno- 
mena, occurred separately and in succession. 
* Chap. v. p. 88 5 and Second Edition, p. 100. 
