MIXTURE OF FORMS IN DEEP SEAS. 275 



observations, in the raised coral-cliffs of Pelelew. Their base, 

 which is everywhere visible, consists entirely of a few species of 

 Lophoseris mixed with other deejD-sea forms; the species of 

 Loplwseris belong indeed to the most delicate forms, and the 

 genvis itself is one of the most fragile of the inhabitajits of the 

 deep sea. The higher and highest portions of the Pelelew cliffs 

 contain on the contrary only Astrseidae, Madrepores, Porites, 

 and similar natives of small depths. And in direct proportion 

 as this structure of the elevated Pelew reef furnishes an argu- 

 ment for its origin during a period of slow upheaval it affords a 

 no less strong one against the hypothesis that it could have 

 been formed diiring a period of subsidence. 



Thus we have reached the end of our enquiry. It has 

 shown us that the subsidence theory ^"^ is insufficient to explain 

 the structure of the Pelew reef, and also that all difficulties dis- 

 appear if we assume that the really efficient influences which 

 have determined the growth of the corals in certain directions 

 operated during a period of slow upheaval. And finally, it has 

 offered a last, grand example of those direct effects of water in 

 motion on the mode of growth of animals, of which, in a former 

 section, I have mentioned other less conspicuous instances. 



