206 CAKBONIFEEOUS VOLCANIC ROCKS OF SOMERSET 
“ Possibly if the vent had been situated in very shallow 
water, or on the land, much of this fragmental material 
would have been blown into the air, fallen in the water, 
and settled down quietly on the sea-floor, as, indeed, appears 
to have been the case with much of the tuff at Middle Hope, 
two miles to the north. At Weston, however, the greater 
weight of water above may have prevented this, and com- 
pelled the fragmental material to flow as lava. Or, again, 
as in the West Indian' examples already cited, the expan- 
sive force of the imprisoned vapours may have been 
sufflcient to break up the lava within the vent, but in- 
sufflcient to do more than just force the tuff over the lip of 
the vent, whence it flowed along the sea-floor in obedience 
to gravity, and impelled forward, in part, by the expanding 
gases. 
“ One of the most remarkable features of the sheet is the 
abundance of lumps and irregular masses of limestone, 
enclosed in the amygdaloidal and ‘ pillowy ’ basalt, or 
occurring as phacoids and lumps in the tuffy material.” 
. . . “ Characteristic features are the concave surfaces of 
the limestone, often due to the fact that the latter occupies 
an irregular space between a number of spheroids or 
‘ pillows ’ of the basalt, looking as if either the limestone 
had been absorbed by the hot lava, or, more probably, 
squeezed into its present shape by the distending and 
moving spheroidal masses. 
“ There can be no doubt that this limestone is not 
secondary, due to the deposition of calcareous material 
from aqueous solution subsequent to the outflow and 
consolidation of the lava ; nor has it been deposited as 
sediment in irregular spaces between the spheroids after 
the cooling of the basalt ; but it is unquestionably part of 
the calcareous floor upon which the basalt-flow rests. 
Many of these included masses are oolitic, the structure 
being visible sometimes to the naked eye, while a micro- 
