ROCKS OF SHROPSHIRE, - 663 
rock. Microscopic examination of a slide of this caused me to suspect 
that it was not a true granite, even before the investigation of Dr. 
Callaway’s specimens and our joint visits to the locality. Besides the 
granitoid rock, there is seen, in the lower portion of a large pit, a com- 
pact greyish rock; both these have here been very fully examined 
with the following results :— 
(A) Compact type-——Five specimens in all have been examined, 
three from different parts of the greyish mass forming the lower 
portion of the pit, two from its upper left-hand corner, where the 
rock has a redder colour and a very fragmental aspect. As regards 
the first three, under the microscope they possess in common far 
more resemblance to the rhyolites described by Mr. 8. Allport than 
one would suspect from their macroscopic aspect*. All, seen by 
transmitted light, have a more or less glassy aspect, and with cross- 
ing Nicols exhibit the usual devitrified structure. For the details of 
this I content myseli with referring to Mr. Allport’s descriptions, 
and will merely call attention to the structural variations in each 
specimen. 
(1) A compact buff-grey rock from the base of the quarry (‘“ fairly 
typical, very jointy”—C. C.). This exhibits a great number of 
somewhat faintly defined crystallites of a rather curved or wavy form, 
such as are figured by Zirkel in the 8.E. corner of figure 4, plate 
vill. “‘ Microscopical Petrography ” (U.S. Geol. Explor. of Fortieth 
Parallel), which give slight indications of a fluidalarrangement: and 
there are numerous minute filmy brown patches of what may be an 
iron mica, both isolated and in clusters, associated with a fibrous 
mineral showing with crossed Nicols a bright golden colour ; minute 
fibres of the same are disseminated over the slide. The white specks 
visible in the rock are probably decomposed felspar; the only one, how- 
ever, on the slide shows spherulitic structure towards the exterior, and 
may be simply a fragment of glass. There are one or two included 
fragment-like bits containing much opacite 7. 
(2) A dull green rock, marbled or spotted with pinkish buff, from 
the upper part ofthe mass. General character fairly similar to last, 
except that in parts a fluidal structure is more conspicuous, and 
there are abrupt changes in the microlithic structure, with compara- 
tively sharp lines of division, as is common in glassy rocks; cracks 
traverse the slide, filled now with microlithic minerals, chiefly quartz ; 
some of the spots, as in the last, are probably fragments in a slightly 
different condition. 
(3) A marbled dull greenish and pale-red rock, also from the 
upper part of the grey mass (‘taken from a place where there is a 
marked concentric spheroidal jointing ”—C. C.). 
Parts of this slide exhibit a beautiful perlitic structure; other 
* The marked difference in colour is due to the fact that the normal Wre- 
kin rocks are full of desseminated opacite and rich red ferrite, while in these 
from the Ereal the corresponding mineral is a pale-brown ferrite. 
+ This pseudo-clastie character, the result, doubtless, of motion after partial 
consolidation, is not uncommon in glassy rocks. Mr. Allport has giyen mea 
most interesting example of it from the other part of the Wrekin. 
