412 PRINCIPLES OF STRATIGRAPHY 



known regarding the rate of growth of the organisms forming the 

 reefs. Experiments and observations on Funafuti reef organisms 

 showed that the lichenous forms of Lithothamnion grow very 

 slowly, no appreciable increase in size occurring in five months. 

 When, however, the alga was killed by too long exposure to the 

 sun at low tide, turning white as a result, a resubmergence caused 

 the pink color to reappear in a few days by the spreading from a 

 center where some cells still remained alive. Halimeda, however, 

 the alga producing the greatest amount of calcareous debris, grows 

 more rapidly, a cluster 3 inches in height and of equal thickness, 

 and weighing 14.38 grains after it was dried, growing in a period 

 of six weeks. 



The rate of increase of Millepora on Funafuti was found to be 

 16.5 per cent, per annum for the massive M. complanata, while the 

 branching M. alcicornis showed an average increase in size of i 

 inch in 34.7 weeks. The latter species also covers objects entangled 

 in its mass, and fragments of Halimeda and other corallines may 

 thus be enclosed. Of the corals. Pontes lirnosa was found to in- 

 crease in weight at the regular rate of 47.27 per cent, per annum. 

 The encrusting coral Hydnophora niicrocona was found to spread 

 at the rate of one inch in 39 months. Astraopora occllata, though 

 forming new calices between the old ones, showed no measurable 

 increase in size during the period of observation. Pocillopora 

 grandis increased in all directions at a rate of one inch in 13.5 

 weeks ; while small pieces of P. verrucosa were found to increase in 

 weight at the startling rate of 150 per cent, per annum. This, how- 

 ever, was partly due to the expansion of the living matter over the 

 broken surface, and the formation of new calices there, a feature not 

 normal under natural conditions. A similar large increase was 

 found for P. pancistcllata. The mushroom coral Montipora in- 

 cognita showed a rate of growth in one direction of half an inch in 

 three months, and an average increase in three directions measured 

 one inch in 35.7 weeks. 



An extensive growth of the coral Orhicella annularis took place 

 upon a bell olive jar and decanter recovered in 1857 from the wreck 

 of a vessel supposed to be the British frigate Severn, lost off Turk's 

 Island in the West Indies in 1793. These specimens are now pre- 

 served in the Museum of the Boston Society of Natural History. 

 (Crosby, i8:2op; Verrill-88.) During the 64 years of submerg- 

 ence Orbicella annularis attached to the bell spread out on all sides. 

 The thickness at the center is about 8 inches and the breadth 15. 

 The olive jar and glass decanter are cemented together by a similar 

 mass of the same species. The wreck lay in from three to ten 



