90 



THE VOYAGE OF H.M.S. CHALLENGER. 



separates Nightingale from Inaccessible, while depths beyond 1000 fathoms occur in 

 some places between Nightingale and Tristan. 



On account of the weather and the difficulty of gaining access to the interior of 

 Nightingale, the Challenger naturalists had to limit their geological collections to the 

 rocks which cropped out near the shore. Nightingale differs greatly in appearance from 

 the other islands of the group, being more varied in outline and surrounded by cliffs 

 only thirty or forty feet high, and often less. The southern part of the island is more 



Nightingale Island, from the North. 



picturesque, the ground rising by successive crests to a peak 1105 feet high, one side of 

 which is almost vertical for half its height. Mr. Buchanan was unable to ascend this 

 hill, but he describes the rock as being greyish in colour, and of a sub-columnar 

 structure. The rest of Nightingale is undulating, and the rocks, except at a few isolated 

 points, are covered with verdure. No traces of recent volcanic activity are to be seen. 

 The rocks of the coast are chiefly a conglomerate or breccia of doleritic fragments 

 embedded in a whitish felspathic mass. Here and there the conglomerate is surrounded 

 by beds of volcanic rock probably of more ancient origin. Marine erosion has hollowed 

 the cliffs girdling the island into innumerable caves, formerly the refuge of seals, which 



