136 
NEWER PLIOCENE PERIOD. 
[Ch. X. 
these shells, which will be found in Appendix II.* The vol- 
cano of Gabel Tor, situate at the entrance of the Arabian 
gulf, is the nearest volcanic region known to us at present. 
We should guard the reader against inferring, from the facts 
above detailed 3 that marine strata of the newer Pliocene period 
have been produced exclusively in countries of earthquakes. 
If we have drawn our illustrations exclusively from modern 
volcanic regions, it is simply for this reason, that these forma- 
tions have been made visible to us in those districts only where 
the conversion of sea into land has taken place in times compa- 
ratively modern. Other continents have, during the newer 
Pliocene period, suffered degradation, and rivers and currents 
have deposited sediment in other seas, but the new strata re- 
main concealed wherever no subsequent alterations of level 
have taken place. 
We believe, however, that to a certain limited extent the 
growth of new subaqueous deposits has been greatest where 
igneous and aqueous causes have co-operated. It is there, as 
we have explained in former chapters, that the degradation of 
land is most rapid, and it is there only that materials ejected 
from below, by volcanic explosions, are added to the sediment 
transported by running water f. 
* These fossils are now in the museum of Mr. Greenough, in London, and du- 
plicates, presented by him, in the cabinets of the Geological Society. 
1* See vol. i. chap. xxiv. • and vol. ii. chap, xviii. 
