13G 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, 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 ta"ken 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. 

 t See vol. i. chap. xxiv. ; and vol. ii. chap, xviii. 



