E. B. Bailey— The Sgurr of Eigg. 299 



general body of the pitchstone, I think it may be taken as established 

 that the felsite has followed closely upon the heels of the pitchstone 

 (so far as a distinction can be maintained) and has been supplied from 

 the same source. 



There will probably be not a few who will regard this evidence of 

 internal intrusion phenomena as the key to the whole problem, and 

 will agree with Harker in considering the pitchstone-felsite mass 

 a composite sill. I confess that before I visited the exposures 

 I ranked the nature of the stratification of the mass as a crucial 

 point of difference between the two disputants. Now I think 

 othei'wise, and remember the late Dr. Tempest Anderson's description 

 of a great eruption of basalt at Matavanu in Savaii, one of the Samoan 

 Islands. The account was given in 1910, when the eruption had 

 been in progress since August, 1905, and the following brief extract 

 will serve as an indication of its bearing upon the matter in hand. 



"In the early part of the eruption the lava did not extend far from the 

 crater, the longest streams not exceeding two or three miles, and these did not 

 present the same appearance as subsequently, but were covered with moving 

 scoriae and stones, so that the whole mountain appeared to be in motion. 

 Later on the lava was often very abundant and very liquid : at times it flowed 

 like a river of water 200 yards wide ; at others, as numerous small streams 

 not above 10 feet wide, and in these cases was often so fluid that it nearly all 

 ran away and only left a fresh crust less than two inches thick, over which it 

 was safe to walk next day. 



" The large fresh lava-fields soon got crusted over on the surface with 

 solidified lava, and the liquid lava continued to flow underneath. Even at the 

 crater it seldom flowed over the lip, but generally entered holes and tunnels in 

 the sides and flowed underground. The lava-field thus became honeycombed 

 with channels of liquid or pasty lava, which occasionally came to the surface 

 and flooded it with fresh sheets of lava ; at other times the surface frequently 

 floated up and was raised by the intrusion of fresh lava underneath, so that 

 what had previously been the course of the valley now became the highest part 

 of the field. Mr. Williams thinks that the lava must be in some places 

 400 feet thick." [5, pp. 624-5.] 



The main lava tunnel at the time of Dr. Tempest Anderson's visit 

 extended as a sinuous line some 10 miles long from the crater to the 

 sea, where it discharged its contents into tlie sea. Its course was 

 marked at intervals by clouds of vapour escaping from fumaroles. 

 Other fumaroles more to the west indicated the position of a minor 

 subterranean channel. 



Let us now turn to a consideration of certain fragmental rocks 

 found in association with the pitchstone, for their importance is, in 

 my opinion, vital. 



Fkagmental Rocks. 



1. A breccia occurs at the base of the pitchstone along the southern 

 face of the ridge for a distance of 500 yards from the eastern 

 termination, and its weathering has given rise to a recess at the foot 

 of the escarpment (YZ, Text-fig. 2). Ilegarding this breccia Harker 

 writes — 



" It shows more or less abundant blocks of the black pitchstone in a soft 

 pale-grey matrix, which is evidently formed by the decay of the pitchstone 

 itself or of its felsitic modification. . . . In addition to the blocks of pitchstone 

 (and felsite), the decomposed matrix encloses in places a few pieces of a blacker 



