204 CARBONIFEROUS VOLCANIC ROCKS OF SOMERSET 
brecciated and very amygdaloidal, with comparatively 
little tuff. But it still contains masses of limestone, even 
larger than those in the middle of the exposure. The 
whole mass appears to consist of great lenticles of basalt, 
or tuff, or both confusedly mixed, together with the in- 
cluded limestone. The median planes of these lenticles 
run obliquely to the limestone beds above and below, so 
that the lenticles dip at a steeper angle than the sheet as 
a whole. It would thus appear that the mass is capable of 
being roughly divided into three portions. Commencing 
at the cliff-end to the north (in which direction the vent 
was probably situated), the rock for the first 30 yards is a 
‘ pillowy ' basalt, with tuff and limestone often occupying 
irregular spaces between the spheroids of amygdaloidal 
basalt ; then, for about 20 yards, the rock is mainly a 
coarse agglomerate, with lapilli and bombs of basalt and 
lumps of limestone ; while for the remaining 100 yards or 
so it is an ordinary basalt coulee, with very few, and always 
small, lumps of burnt limestone.” 
Then follows a section devoted to some special charac- 
ters of the basalt-sheet : — 
“ The characters of this igneous flow which are of 
especial interest are (a) the ‘ pillowy ’ structure, together 
with the tuffy or agglomeratic structure ; and (h) the in- 
cluded lumps and masses of limestone. The pillowy, oval 
or spheroidal masses of basalt, 2 to 8 feet across, usually 
very amygdaloidal, especially round their periphery, and 
sometimes containing small oval or angular cores of a 
slightly different and earlier lava, are usually embedded 
in a tuff made up of lapilli up to 2 or 3 inches across. Near 
the middle of the sheet, covered and underlain by massive 
lava, is a mass 5 to 6 feet wide, with a dip roughly parallel 
to the other lenticular masses, consisting of a confused 
mass of coarse tuffy material, made up of angular frag- 
ments of lava 1 to 2 inches across, imbedded in a fine red 
