1845.] GEOLOGY OF TIA-USU. 319 



gales of wind or earthquake. On the summits of some 

 of the flat rocks, long grass, similar to that usually 

 noticed on rocks frequented by sea birds, was found, but 

 no shrubs or trees. The rocks were everywhere whitened 

 by the dung of marine birds, comprising the Booby, 

 (Pelicanus Sula,} Frigate Bird, (Pelicanus Aquilus,} and 

 various Tern, (Sterna), the noise from which, intended 

 to frighten us from their eggs, was almost deafening. 

 Tia-usu appears to be composed of huge boulders of a 

 greenish porphyritic stone, probably a Basalt, cemented 

 by coralline and amygdaloidal matter, the upper surface 

 being loose plates of greyish Basalt, occasionally cemented 

 by the same amygdaloidal mortar. Some distressed beings 

 had evidently visited this island, not Europeans, as their 

 temporary beds were constructed of materials which 

 belonged to canoes, palmetto thatch, &c. They had 

 probably selected this cave as furnishing water by per- 

 colation from above, and were probably sustained by the 

 bodies and eggs of the sea-birds which abound in the 

 brush wood. In addition to the sea-birds noticed on 

 Pinnacle Island, we found here the gigantic Petrel in all 

 its stages. At the first discovery of the young in its 

 unfledged state, I had some idea that I had been fortu- 

 nate enough to hit upon a specimen of the long-extinct 

 Dodo, but on proceeding further, I found the parent to 

 differ materially from both that and the Solitaire. The 

 capping of this island, from about sixty feet to its sum- 

 mit, which is about six hundred feet above the level, is 

 covered with a loose brushwood, but no trees of any size. 

 We now sought Raleigh Rock, situated to the 

 eastward, but were equally unfortunate in the want of 



