The Scottish Naturalist. 85 



eruptions, as the plants have been identified by paleontologists as 

 belonging to the Miocene or middle Tertiary period. 



When the last sheet of basaltic lava had been ejected from these 

 Hebridean volcanoes their time of great activity was ended. Long 

 ages afterwards the hills and valleys, which denudation had carved 

 out of the basaltic plateau, trembled at the shock of the earthquake, 

 and resounded to the roar of craters, while fiery torrents poured 

 themselves down the hillside ; but these phenomena were quite 

 insignificant when compared with those of the previous eruptions. 

 The great basaltic volcanoes had long been silent, and had been 

 mostly removed by denudation when little parasitic cones formed on 

 the wasted remains of their mighty predecessors sent forth these 

 comparatively tiny streams of acid lava. It is to this final display 

 of volcanic energy that the rock of the Scuir is to be attributed. 



The Scuir is entirely composed of beautifully formed columns of 

 pitchstone-porphyry, which are usually vertical, but are often found 

 lying at every conceivable angle. The earliest observers at once 

 recognised it to be different from the main mass of the island, and 

 were in consequence greatly puzzled to account for it. In en- 

 deavouring to do so they suggested some ingenious theories. 

 Considering that dykes of pitchstone are of frequent occurrence 

 in Eigg, it is not surprising that they considered the Scuir to be a 

 gigantic intruder of this kind. They supposed that, at one time, 

 that basaltic plateau was as high, at least, as the top of the Scuir, 

 and that the pitchstone burst up through it ; at once forming and 

 filling up a vast crack in the basaltic beds, and that by-and-bye 

 denudation removed the surrounding rocks leaving the harder and 

 more intractable rock of the Scuir behind. Both M'Culloch and 

 Hugh Miller adopted this not unreasonable hypothesis. 



It was, however, reserved for Dr. Archibald Geikie to find the 

 true solution of the problem, which he did in the following inter- 

 esting manner. An excavation was made under the Scuir where 

 the pitchstone-porphyry comes in contact with the basalt, when he 

 discovered that the Scuir is underlain by a conglomerate ; an ex- 

 amination of the constituents of this conglomerate proved it to be 

 the bed of an ancient river, a river, moreover, which had flowed a 

 long way, from the northward through a forest-clad land ; for em- 

 bedded in the conglomerate were pieces of wood, twigs and leaves ; 

 while it was partly composed of Laurentian gneiss and Cumbrian 

 sandstone, indicating that the river had probably flowed from the 

 north Highlands where these formations are well represented, 

 through a vanished land whose place is now, for the most part, 



