Oct., 1889. 
PETROLOGY OF LOCAL PEBBLES. 
239 
(23) A coarse asli from Catspool, might have come 
out of the quarry in the Lawrence Hill at the Wrekin. In 
addition to fragments of the splierulites as in the last 
specimen of fragments showing perlitic structure, there occur 
vesicular—or what has been vesicular—basalt apparently, 
the vesicles being now filled with a green mineral. Another 
fragment is andesitic in its character. 
(24) The grey felsites I have principally met with on the 
southern side of the district, but a very greenish-grey rock, 
showing fine flow-banding, and occasional beautiful “flow” 
round included knots or crystals, was obtained at Hamstead. 
Another extremely similar, except in the absence of so many 
quartz grains and its rather less perfect flow structure, was 
collected at a little pit just by the tunnel, between Alvechurch 
and Tardebigg, at a place called on the Ordnance map Ox 
Leasows. The flow lines are accentuated by the presence of 
a greenisli-blue mineral, with dicliroism in many parts, 
changing to a pale yellow on rotating over the polariser. 
It certainly does not appear to have the very high double 
refraction of epidote, yet in its radiating habit of growth in 
the larger masses it has a good deal the appearance of this 
mineral. 
(25) At Catspool was collected a beautiful grey felsite, 
with white splierulites all through it, plainly visible to the 
naked eye (No. 45). 
The structure of the splierulites is not radial, but 
irregularly disposed brushes of crystals fill up the areas. 
They often include the minute crystals of felspar, which 
occur to a large extent in the ground mass of the rock. 
These are mostly very fresh and transparent, as are also the 
larger porpliyritic crystals. The felspars are usually only 
simple twins, and do not show the repeated twinning 
characteristic of the plagioclases, but the fact that in a few 
cases symmetrical extinctions on each side of the composition 
plane were observed, proves the presence of plagioclase, 
which the angles observed would suggest to be oligoclase. 
One of the larger felspar crystals shows extreme 
irregularity of outline; it has either been deeply eaten into 
by the still molten magma, or its growth was crippled. 
(26) Of a somewhat different type is a specimen (44) 
which I found lying by the roadside on the road between 
Alvechurch and Blackwell. 
In the hand specimen the ground mass is very similar in 
colour. Abundance of felspar crystals of J to jLin. long are 
visible, and a number of dark-coloured, elongated masses 
