The Scottish Naturalist. 83 



points of eruption ; so, in all probability, this outflow did not 

 cover the plain so completely as those of subsequent eruptions ; 

 still, from the near proximity of the volcano of Rum, it is not 

 likely that Eigg escaped the fiery deluge altogether ; and in fact, 

 as has been stated, acid lavas are found at more than one point in 

 the island, necessarily but insignificant remains of the original 

 lava stream. By-and-bye these volcanoes quieted down and be- 

 came extinct, or at least dormant, and remained so for a very long 

 time, so long, indeed, that not only were the cones of the craters 

 completely removed, but the very subterranean sources of these 

 volcanoes were dissected and laid bare by denudation. This can 

 be well observed in Mull, where the lavas of the second outburst 

 are seen to be in contact with the deep-seated rocks from which 

 these early lavas flowed. 



The second eruption or series ot eruptions of these volcanoes 

 appears to have been on an enormous scale, and to have lasted, 

 with very considerable interruptions, through a great period. Not 

 only were immense crater cones formed, but lava streams of great 

 volume flowed out for many miles around them, so that the whole 

 plain was gradually buried for many hundreds of feet under sheets 

 of these lavas. 



The lavas of the second eruption were all of the basaltic type, 

 which are of great density and fluidity, and flow freely outwards 

 from their sources. 



It was during this eruption that practically the whole mass of 

 Eigg was laid down. From the volcano of Rum vast sheets of 

 lava flowed out over the plain, probably until they came into contact 

 with similar streams from the other volcanoes. In this way more 

 than 2,000 feet of basalt must have been piled up sheet above sheet 

 over all the area described. In many of the fine natural sections 

 in Eigg the successive sheets and their varying character are well 

 exposed to view. 



Seme of our most distinguished geologists have expressed the 

 opinion that the basalts of the Hebrides were not ejected exactly 

 in the manner I have endeavoured to describe, that is to say with 

 the usual symptoms and accompaniments of volcanic activity, but 

 were thrown out on the surface of the earth by what are called 

 " fissure eruptions ; " and that the lava simply flowed out from 

 fissures without the formation of craters or the ejectment of scorial 

 or other volcanic fragmental debris. On the other hand, quite as 

 competent geological authorities maintain that no eruption of lava 

 has taken place without these accompaniments either in the 



