664 PROF. T. G. BONNEY ON THE MICROSCOPIC 
parts groups of spherulites, with radial structure, some being about 
03 inch in diameter. 
To avoid repetition it is enough to refer to Mr. Allport’s descriptions 
and plate (Joc. cit. pl. xx.)*. 
(4) and (5) are taken from the upper part of the pit on the left- 
hand side. ‘They are much redder in colour than the others, are more 
like the granitoid rock, and have a very fragmentalaspect. A glance, 
however, at the slides under the microscope shows that they exhibit 
the usual aspect of a devitrified glass, with a rather brecciated 
structure, of the character already described, both specimens show- 
ing indications of finidal structure. In the one this is very clear; 
in the other, more or less perfectly developed spherulitic structure in 
frequent. Aiter a careful study of these various slides, and com- 
parison of them with my collection from other parts of this district, 
I have no hesitation in asserting that the compact rock of this pit is 
only the Wrekin rhyolite somewhat altered by various subsequent 
chemical changes, and that it must be regarded as intrusive in the 
granitoid rock. 
(B) Granitoid type—Of this I have had five slides prepared from 
specimens taken from various parts, from the lowest to the highest 
exposures. All may be described as consisting mainly of quartz and 
felspar, with a little iron peroxide (species uncertain) and a yery 
small quantity of chlorite (?). The quartz contains many very 
minute enclosures; the felspar is rather decomposed, and stained 
with ferrite ; orthoclase and plagioclase (? oligoclase) are both com- 
mon; and there is much cross-hatching and interbanding visible. 
Some grains rather resemble microcline. Indications of graphic 
structure, especially on a minute scale, arenot rare. As regards the 
specimens from the middle part of the mass, I cannot venture to 
express a positive opinion; they are very like a variety of granite, 
and yet there is a something, impossible to express in words, which 
reminds me rather of the granitoidites of the “ Dimetian” series in 
Wales than of true granitic rocks. The specimens, however, from the 
bottom part of the mass (as may even be seen by the unaided 
eye) are certainly clastic. Rather rounded fragments, consisting of 
quartz and felspar, often exhibiting a minute graphic structure, are 
imbedded in a matrix containing smaller fragments of quartz, often dis- 
tinctly angular, and of felspar; the matrix also appears to be composed 
of these two minerals, in an extremely fine state of division, but often 
showing an approach to graphic structure. One of two explana- 
tions is alone possible: either the granitoid rock has been crushed 
in situ (owing probably to the intrusion of the rhyolite); or we 
have here a quartz-felspar grit, which, though highly metamorphosed 
(the more finely divided constituents having crystallized in situ), 
still retains traces of its original structure. 
After the best consideration which I can give to the question, I 
* Thbelieve this is the first time that perlitic structure has been noted at 
the Wrekin. Mr. Allport’s specimens were all from Lea Rock, where spherulitic 
structure also is much more common. I have since found specimens in this 
Ercal pit showing to the unaided eye very distinct spherulitic structure. 
