332 DR. G. J. HINDE. 



greater part of the rock, and between 652-660 feet in the Main Boring they are the 

 main^-constituents of the cores. As a rule their structure is well-preserved, so that 

 they are readily recognised in microscopic sections. The specimens in the Lagoon 

 Boring have been determined by Miss Barton"' (Mrs. Gepp) to belong to H. opuntia, 

 Lam., var. macropus, Askenasy. According to Mr. Finckh, Halimeda is remarkably 

 abundant both on the present floor of the lagoon and on the ocean slopes of the reef at 

 Funafuti. 



Genus Lithothamnion, Philippj. 



This genus is represented in the different borings by branching, nodular, and more 

 especially by encrusting forms, which grow over corals and other organisms so as to 

 form layers of very compact dense rock. Li many parts of the borings, particularly 

 between 730-1100 feet of the Main Boring, Lithothamnion materially contributes to 

 the cores. In the recent examples of calcareous algse from Funafuti, Professor Foslie 

 distinguishes, besides Lithothamnion , tw^o other allied genera, Lithophyllum and 

 Goniolithon, but in the fossil forms enclosed in the solid cores it has not been 

 practicable to recognise the distinctive characters of the two latter genera, and they 

 have therefore been all placed under Lithothamnion, 



(8) Summary. 



Of the borings carried out at Funafuti with the object of investigating the 

 structure of a coral reef, the most important is that known as the Main Boring, 

 which reached a depth of 1114|^ feet. The two earlier borings, which had to be 

 abandoned after reaching 105 feet and 75 feet respectively, were practically similar 

 to the corresponding depths of the Main Boring. The two borings in the lagoon, 

 situated near each other, penetrated to 113 feet and 144 feet helow the floor of the 

 lagoon, the depth of water at the spot being 101 feet. 



In the Main Boring, for a distance of 748 feet from the smface or about two-thirds 

 of its depth, the greater part of the rock passed through was either unconsolidated 

 or so lightly cemented that in the process of drilling about nine-tenths of it was 

 reduced to granular and powdery fragmental material and the remaining tenth was 

 solid hard limestone. The lower third of the boring, from the level of 748 feet to 

 the bottom at 1114 feet, consisted almost entirely of dolomite or dolomitic limestone 

 sufliciently hard to yield a ])ractically continuous solid rock-core, with a total length 

 of 311 feet, or 85 per cent, of the distance passed through. The rock throughout 

 the boring is either limestone or dolomitic in character ; no silica has been observed, 

 and there are no traces of pumice or other volcanic products. The rock cores do not 

 show any distinct evidence of stratification. 



The rock appears to be entirely of organic derivation, consisting principally of 

 the skeletal remains of corals and foraminifera with calcareous algae belonging to 



* ' Linnaean Soc. Journ.,' Botany, vol. 34, 1900, p. 481. 



