378 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



known. A fairly good view of this part of the island was 

 obtained from the top of a cliff at Chatham Bay, and it 

 appeared to be made up of a broad table-land heavily covered 

 with vegetation, as are the remaining portions of the island. 



Rock-exposures occur along the banks of streams and along 

 the sides of perpendicular cliffs. So far as could be observed, 

 the rocks are basaltic in character. Columns of basalt occur 

 frequently near sea-level, and caverns of considerable depth 

 have been formed in many places by the action of the waves. 

 The soil is composed for the most part of a sticky yellow clay 

 and vegetable mold. From the more exposed places the mold 

 has been washed off, leaving the clay bare. On the steep sides 

 of the mountain erosion is rapid. In the small valleys one 

 often encounters large forest trees which have been dislodged 

 from the steep hillsides above by the washing away of soil 

 from the roots to such an extent that they could no longer 

 maintain their position. Land-slides are rather frequent, and 

 when they occur, large quantities of earth and boulders are 

 brought down along with the vegetation which covers the 

 area. After a land-slide Ipomoea cathartica seems to be one 

 of the first plants to invade the denuded area, followed by 

 Hibiscus tiliaceus. 



The island lies in the moist tropical belt, and has a large 

 amount of rainfall, the exact amount of which is not known, 

 but it probably amounts to several feet per year. May, June, 

 and July are said to be the rainiest months, and January, Feb- 

 ruary, and March the driest. It rained eight out of the eleven 

 days we were on the island, and some of the rains during this 

 time were much harder than those which occur in more tem- 

 perate regions. According to Captain Gissler the temperature 

 ranges from 68° to 92° F. 



Halophytic plants are very few in number, possibly because 

 of the precipitous nature of the shores in most places. Ipo- 

 moea Pes-caprae is the most pronounced halophyte, and it 

 occurs only to a limited extent on the sand beaches at Wafer 

 Bay. Hibiscus tiliaceus forms small groves near the beach in 

 a few places ; and Clusia rosea often forms dense thickets along 

 the sides of the cliffs some distance above the water, sending 

 down absorbing roots into the sea. At several places near the 

 shore there are small groves of Cocas nucifera, the nuts of 



