io ANNALS OF SCOTTISH NATURAL HISTORY 



present Peregrine Falcon and from the casual visits of the 

 Merlin. There is no cover elsewhere, unless some short 

 narrow runnels connecting a series of diminutive pools on 

 the exposed plateau can be regarded as such. 



The rocks forming the island consist of several varieties 

 of Lewisian gneiss, traversed by numerous veins of granite, 

 pegmatite, and hornblende. They show evidence of con- 

 siderable disturbance, being crumpled, and twisted, and 

 tossed up and down, in a most remarkable manner. 



There are three ancient buildings on the island. The 

 chief of these resembles a large dog-kennel, and is supposed 

 to have been built for ecclesiastical purposes, and is called the 

 " Blessing House " on the Ordinance Map. The other two 

 are Brochs, each with two square chambers, and surmounted 

 with a bee-hive-shaped roof. 



The islands are resorted to annually, as breeding stations, 

 by hosts of marine birds, chief among which, in point of 

 numbers, is the Puffin ; and the most interesting, from an 

 ornithological point of view, the Fork-tailed Petrel and the 

 Fulmar. 



Ornithologically, however, the islands are chiefly remark- 

 able on account of the streams of birds of passage which 

 sweep over them in both spring and autumn, when en route 

 between their northern summer and their southern winter 

 homes. These streams are surprising for their magnitude, 

 both in individuals and species, when the far western situation 

 of the islands is taken into consideration. The result of 

 our investigations on these interesting western movements 

 was most satisfactory and much valuable information was 

 obtained, but further researches elsewhere will have to be 

 undertaken ere the results are ripe for publication. The 

 lantern throws out three slowly revolving beams, each of 

 140,000 candle power ; but during our stay few birds visited 

 the light, the weather conditions being almost uniformly 

 unfavourable for " a night at the lantern." We were some- 

 what surprised to find that, so far as we could ascertain, 

 no birds seemed to visit the island from Lewis and Harris 

 during our stay. Thus we never saw a single Starling a 

 species which is abundant in the Outer Hebrides, and much 

 given to wandering in the autumn ; and only a single 



