248 
THE TERTIARY VOLCANOES 
BOOK VIII 
the close of the volcanic period will be the subject of a special chapter in a 
later part of this volume, I cannot here refrain from calling attention to the 
pitchstone of Eigg and Hysgeir as one of the most impressive monuments of 
denudation to he found within the British Isles. Though now so prominent 
an object in the West Highlands, this rock once occupied the bottom of a 
' alley worn out of the basaltic tableland. Prolonged and stupendous denu- 
dation has destroyed the connection with its source, has cut down its ends 
into beetling precipices, has reduced the former surrounding hills into 
gentle slopes and undulating lowland, and has turned the bottom of the 
ancient valley into a long, narrow and high crest. Moreover, we see that 
the erosion has not been uniform. The great wall of the Scuir does not 
stand fairly on the crest of the basalt-plateau but on the south side of it, so 
that the southern half of the old valley, with all its surrounding hills, has 
been entirely cut away. That subsidence has also come into play in the 
destruction of even the youngest parts of the volcanic plateaux will be more 
fully discussed in a later chapter. I need only remark here that the sub- 
mergence of Hysgeir probably points to extensive depression of the land- 
surface on which the lavas were poured out. 
