260 



are only 60 feet high. They want, however, the regularity and the 

 defined forms which the rocks at StafFa present ; but they have less 

 of the dark and gloomy aspect of the latter. They are covered with 

 innumerable tribes of birds, especially gannets or solan geese, gulls, 

 cormorants, auks and puffins. The firing of a gun caused the air to 

 be darkened by the birds. The young geese are prized by some as 

 an article of diet, and a rent is paid for them. They require to be 

 cooked in a particular manner in order to render them at all palatable. 

 The tacksman of the island employs people to capture the young 

 birds, and there is no small risk incurred in doing so. We saw some 

 men engaged in taking the birds on a narrow ledge of rocks, which 

 they had reached by being let down by ropes from the summit. Every 

 now and then the rocks crumble and give way, so as to add much 

 to the danger of this perilous undertaking. 



The rocks of the island consist of a porphyritic sienite, which is 

 sometimes amorphous and sometimes columnar. The basis is felspar, 

 with small grains of quartz and sometimes hornblende interspersed. 

 We observed numerous trap veins traversing the rocks, and occasionally 

 fine caves are formed. One of these caves occurs towards the north- 

 ern part : it is about twelve feet wide, between twenty and thirty feet 

 in height and extends about fifty feet. Asplenium marinum lined its 

 walls, and near its entrance magnificent specimens of Cochlearia offi- 

 cinalis were picked, with the leaves 4^ inches in diameter. The lux- 

 uriance of this and the other plants in the island may depend in pai't 

 on the dung of the sea-fowl, which serves as excellent manure when 

 applied in moderate quantity. At the foot of some of the cliffs there 

 is a large accumulation of black mould, mixed with the dung of sea- 

 fowl and the remains of niunerous birds that have fallen from the cliffs. 

 The ammoniacal odour arising from these sources under the influence 

 of the sun's rays, was very powerful. The wet nature of the climate 

 prevents the guano from accumulating in large quantity so as to ren- 

 der it an object of importance. Some of the soil was analysed by Dr. 

 R. D. Thomson, and was found to contain a notable quantity of am- 

 monia. Where the guano existed in the greatest quantity there was 

 scarcely any vegetation, and it was only where the manure was spar- 

 ingly applied that the plants assumed the luxuriance which I have 

 described. 



On the rocks in the south of the island we picked Lavatera arborea 

 and Sagina maritima. The former of these plants occupies many in- 

 accessible ledges on the cliffs, and it is curious to remark that it is 

 found both on the Bass rock and on Ailsa. Raphanus maritimus was 



