;>60 H. B. GUPPY/ ON THE RECENT 



An inspection of the diagram referring to the north coast of Santa Anna will 

 show that probably the underlying soft deposit is not much over 30 feet in 

 thickness in that locality. 



The various stages in the movement of elevation which this island has 

 passed through since it first appeared at the surface of the sea are worthy of 

 notice. There was a time in its history when the present summit alone 

 appeared at the surface of the sea as a tiny atoll encrusting a submerged 

 volcanic peak, the remains of which still exist in the shallow basin on the 

 summit before referred to. Then succeeded a period of upheaval, during which, 

 without any lengthened pause, this tiny atoll was raised to a height of from 250 

 to 300 feet above the sea. This was followed by a prolonged interval of rest 

 during which the main atoll was formed, differing however from the typical 

 atoll in that a pinnacle-islet rose up abruptly to a height of nearly 300 feet 

 from the middle of the east side of the reef. Then commenced another long- 

 period of elevation, prolonged to the present time, during which the rim of the 

 atoll has been raised 200 feet above the sea, the waters of which have been 

 excluded altogether. There were pauses during this stage of elevation, the 

 most marked being midway in the stage when that portion of the rim on the 

 south side, which is only 100 feet above the sea, was formed. But in the lower 

 levels, wherever the land descends by a gentle slope to the coast, the retro- 

 cession of the sea may be traced in the successive linear heaps of coral masses, 

 1 to 2 feet in height, which mark slight pauses in the elevation. The most 

 recent upheaval is shown in an ancient line of erosion removed usually from 5 

 to 8 feet above the present line of wave-action. Where the coast is cliff-bound, 

 the present and ancient lines of erosion are displayed in the faces of the cliffs ; 

 but where the coast is low, the old sea-level is to be found in a line of erosion, 

 often worn back into caves, displayed in the base of a line of inland cliffs which 

 are removed at distances varying from a few paces to a hundred yards from the 

 beach, a low strip of recently elevated land supporting cocoa-nut palms and 

 other vegetation intervening. 



In concluding this reference to Santa Anna, I will make a few observations 

 on the small adjacent island of Santa Catalina, which from its profile has 

 evidently experienced the same stages in the upheaving movement, which Santa 

 Anna has undergone during its last elevation of 200 feet. Santa Catalina is a 

 low level-topped island elevated about 180 feet above the sea. Here, we have 

 another ancient and originally submerged volcanic peak, which, having become 

 encrusted by coral reefs, has been upheaved to a height of nearly 200 feet above 

 the sea. Although the coral rock apparently forms the whole island, it is in 

 reality but an outer crust, investing as a nucleus some ancient peak once sub- 

 merged. In the beds of two small streams on the summit, I found exposed in 

 mass a breccio-conglomerate formed of fragments of various volcanic and 



