266 
THE FLORA OF WARWICKSHIRE. 
It is at any rate pretty well established that a molten sili¬ 
ceous magma from which crystals are separated in the process of 
cooling will become progressively richer in silica and alkalis 
and richer in potash relatively to the soda. 
It is quite possible that we have in this phenomenon a 
hint as to the reason of rocks of progressively more acid 
character being formed in a given volcanic district, as is so 
frequently the observed fact. If a lava of medium acidity is 
being erupted it is conceivable that if the heat by which it 
has been kept fluid in the interior of the earth is so far 
reduced as to permit of crystallization taking place, any 
further eruption may only be able to bring to the surface the 
more acid, still fluid, residue, and by this means the character 
of the resulting rock masses would be gradually changed. 
The succession andesite, trachyte, rhyolite with increasing 
degrees of acidity is frequent in volcanic regions. In the 
foregoing remarks I have made use of the paper by Mr. Teall, 
in the “ Geological Magazine ” for March, which I have 
previously quoted, as the question is one of much interest,and 
I think our Rowley veins have a definite bearing on the 
subject as showing to what a great extent the differentiation 
of a cooling magma may proceed. 
THE FLORA OF WARWICKSHIRE. 
AN ACCOUNT OF THE FLOWERING PLANTS AND FERNS 
OF THE COUNTY OF WARWICK. 
BY JAMES E. BAGNALL, A.L.S. 
(Continued from page 235.) 
GRAMINA.— Continued. 
BRACHYPODIUM. 
B. sylvaticum, 11. and S. False Wood Drome Grass. 
Native : On hedge banks and in woods. Common. July, August. 
Area general. 
B. pinnatum, Beauv. Barren False Brome Grass. 
Native: On hanks, roadsides, and field borders in calcareous soils. 
Local and rare. July, August. 
