CARBONIFEROUS VOLCANIC ROCKS OF SOMERSET 201 
Massive limestone full of fossils. The lowest three feet of the 
rock are crowded with fine volcanic dust, which under the micro- 
scope is seen to consist of fine vesicular lapilli. 
Highly amygdaloidal altered basalt, having a ‘ pillow ’-structure 
and with abundant calcareous and hsematitic veins, and threads of 
carbonate of copper ; about 35 or 40 feet. 
Red limestone, full of fine volcanic dust, and passing down into 
the ordinary grey fossiliferous limestone. 
“ This section places clearly before the mind the succes- 
sion of volcanic events of which it retains the record. 
From some vent in the neighbourhood fine dust continued 
to be ejected during a considerable interval, for the lime- 
stone, through some 30 or 40 feet of its mass below the 
basalt, is full of disseminated volcanic particles. The 
lapilli abound in vesicular basic pumice, and show the 
prevalent dull-green palagonitic modification of what was 
no doubt originally a basic glass. 
“ At last a stream of lava flowed over this part of the 
sea bottom. It rested immediately on the calcareous 
sediment to which it is now firmly bound, and which is 
highly crystalline ; but there is no conclusive evidence that 
this crystalline structure has been due to the heat of the 
overlying lava. This lava is now much oxidised and 
decayed, strongly amygdaloidal, and presenting the charac- 
teristic ‘ pillow ’ or sack-like structure that has been so 
frequently observed among the submarine volcanic erup- 
tions of former geological periods. The interstices be- 
tween the large irregularly shaped pillow-like masses of 
the sheet have been filled up with calcareous material, 
which, in the form of a network of limestone ribs with 
veinings of haematite, traverses the rock. The basalt 
contains also lumps of limestone, while some of its more 
solid parts have been broken up and have been involved 
in portions possessing a much more slaggy structure. The 
bottom of the sheet is much brecciated, the fragments 
being finely vesicular. 
