NARRATIVE OF THE EXPEDITION IN 1896. 15 



Since the fragments of the hard rock, whicli forms the floor of the islands, thns slope 

 in one direction, i.e., from lagoon to sea, and since this is the direction which 

 Irao-ments now assume under the action of the ocean waves, we are led to conclude 

 that there was once a period in the history of the atoll when neither outer ridge nor 

 lagoon mound were in existence. The ocean then washed riolit across the reef into 

 the lagoon, driving before it corals, whole and in fragments, and other calcareous 

 debris to form the superficial hard crust, A^^hich sujjports the islets, and extends from 

 under them as the remainder of the reef now awash between tides (fig. 7). 



mean levet tide 

 ow level tide 



Fig. 7. — In illustration of the mode of origin of the rock, which forms the basis of the islets, and 



encrusts the summit of the Atoll. 



A second feature of equal importance is the occurrence of pinnacles of hard rock 

 projecting from the shore platform (fig. 4, D), and rising above the waves at mid- 

 tide like a miniature sea- stack. It was with no little surprise that I encountered one 

 of them on taking my first walk along the ocean beach ; it stood some four or five feet 

 high, and the sea was breaking upon it heavily, bursting over it in great fountains 

 of spray ; the comparison with a sea-stack was inevitable, equally so the inference 

 that the ocean platform is a plain of marine erosion ; and in my notes written at the 

 time I find a sentence to the following effect : "If this be so, some important change 

 must have occurred since the coral breccia was formed and consolidated. Tavo views 

 are possible, one that the pinnacle represents the core of an ancient outer ridge, 

 which by a depression of the island or otherwise has been brought within the 

 denuding action of the waves ; the other, that it may be the surviving part of an 

 ancient reef, which has been elevated and denuded since its growth." 



Similar pinnacles were subsequently observed in numerous localities, and they 

 came to be regarded as common characters of the reef; they are met with frequently 

 at the ends of the islets (fig. 8), but also along their face, sometimes they form a 

 linear series, and sometimes are replaced by a more or less continuous line of clifl', 



Fig. 8. — Pinnacles of coral-rock at the extremity of Pava islet. 



especially on Funafuti islet. They are dry at low tide, and not completely submerged 

 at ordinary high-tide level, above which they project some two or three feet. The 

 lower part bears obvious marks of marine erosion and is usually imdercut ; the upper, 

 exposed to sub-aerial agents, is fretted into complicated and fantastic forms, partlv 

 due to the weathering-out of the corals which enter into its constitution. 



