•2(U 



THE VOYAGE OF H.M.S. CHALLENGER. 



Tussock. This was a great Penguin road, for the whole place was one vast Penguin 

 rookery, and the grass that looked like turf was higher than a man. 



The rocks of Nightingale Island are augite-andesite passing to amphibolic andesite 

 and tufa of the same rocks. The caves in the low cliffs are so numerous as to form a 

 striking feature in the appearance of the island as it is approached, and indicate an 

 elevation of the island ; they are not apparent, however, at Inaccessible or Tristan 

 Islands. The caves, with the sloping ledges leading up to them, are frequented, as was 

 said, by Fur Seals. Four years before the visit of the Expedition, 1400 seals had been 

 killed on the island by one ship's crew. Seals were very much scarcer in 1873, but the 



Fig. 104. — Nightingale Island from the North. 



island was visited regularly once a year by the Tristan people, as was also Inaccessible 

 Island. The Germans only killed seven Seals at Inaccessible Island during their stay, 

 but the Tristan people killed forty there in December 1872. 



At the entrance to the rookery the hard rock was actually polished, and had its 

 irregularities smoothed off where the feet of the birds had worn it down at the commence- 

 ment of the street. No doubt the Diatom skeletons present in the food and dung of 

 the Penguins, and always abundant in the mud of their rookeries, adhering to their 

 dirty feet, act as polishing powder and assist the wearing process. The street did 



