394 PRINCIPLES OF STRATIGRAPHY 



with those growing on the outer reef. In addition to them are nu- 

 merous species such as Seriatopora stricta, Mtissa corymhosa, 

 Favia lobata, Fungia dentata, and many others that are not found 

 on the outside." This is due to the fact that these corals are either 

 free (Fungia) or attached by such slender stems that they could 

 not maintain themselves in the strong surf and currents of the open 

 ocean. 



Within the lagoon these species grow close together and form 

 knolls and patches, which, together with the clastic debris washed 

 into the lagoon, tends to fill it up completely. The distribution of the 

 organisms in the atoll of Funafuti in the Ellis Island group (long. 

 179° E. and lat. 8° 30' S.) may be taken as representative (Finckh- 

 31). "On the ocean side up to as far in as the wash of the waves 

 reaches at low-water spring tide, the reef platform is densely cov- 

 ered with vigorously growing organisms." A thinly branching 

 Lithothamnion is the most abundant, appearing in small, isolated 

 shrub-like clusters, from i to 5 inches in diameter and varying simi- 

 larly in height. Between these grow small Madrcpora loripes, 

 Brook. On the outer edge of the platform lichenous and knobby 

 Lithothamnia occur, but no Porites nor Heliopora cccrnlea. None 

 of these species forms patches of great size, owing to the intense 

 intraspecific struggle for existence which takes place here, though 

 eventually Lithothamnion seems to be the victor over the corals and 

 hydrocorallines. This vigorous growth extends for only 2 or 3 

 feet downward at the edge of the reef below the level of low-water 

 spring tide, below which the reef becomes comparatively destitute of 

 organisms. 



The Lithothamnion zone is dissected by a large number of nar- 

 row cross channels, which give it a fringed appearance. The edge 

 is generally somewhat raised and rough on account of the Litho- 

 thamnion growth, and the encrustation of the surface by Foramin- 

 ifera, like Carpenteria and Polytrema. This feature is less marked 

 or wholly absent on the lagoon side of the coral reef platform. Dif- 

 ferent species of Lithothamnion characterize this fringe in dififer- 

 ent parts of the atoll. Thus in the eastern or windward portion a 

 lichenous form abounds, while in the western or leeward portion 

 of the lagoon rim a thinly branching species and another lichenous 

 form with stony knobs entirely replace the first species. 



Next to the Lithothamnion, the branching nullipore Halimeda 

 abounds on the reef, both on the lagoon and ocean slopes. It lives 

 to the 45-fathom level, while the Lithothamnion has been found 

 alive at 200 fathoms' depth. The hydrocorallines are chiefly repre- 

 sented by the branching Millepora alciconiis and the more massive 



