STRUCTURE OF SOME SHROPSHIRE ROCKS. 665 
incline to the former view. But whether this rock be a granite or a 
granitoidite (and I believe it the latter), there can be no doubt that 
it is far older than the rhyolite, and thus we may regard it as, in 
general terms, a representative of the ‘ Dimetian ” series. 
(C) A very similar rock occurs at Primrose Hill, just 8. of the 
Wrekin. ‘Two specimens collected by Dr. Callaway, labelled 
“summit” and ‘“N.W. slope halfway up,” in mineral constituents 
and general character so closely resemble the Ercal rock, that we 
need not hesitate to class them as belonging to the same series. 
The former, in structure, is similar to the specimens from the middle 
part of the Ercal granitoidite; the latter exhibits a clastic struc- 
ture very distinctly in parts of the slide; so that here also we must 
suppose a most exceptional case of local crushing or admit a clastic 
origin. 
Gneiss, Primrose Hill.—The slide was cut from a specimen whose 
banded structure showed even to the unaided eye that it was a 
gneiss. Microscopical examination proves it to be a most character- 
istic example : it consists of irregular quartz grains with the inter- 
stices often occupied by a granular mineral (ofa dull yellowish colour 
with transmitted light, and rather brilliant tints with crossing 
Nicols), probably a secondary product and possibly epidote, with fel- 
spar, mica, and a greenish chloritic mineral. ‘There is the usual ten- 
dency on the part of the different constituents to collect in bands. 
The rock is not yery rich in felspar; some of this is very character- 
istic microcline. ‘lhe mica is colourless with transmitted light, and 
shows very brilliant tints with the Nicols. The green mineral rather 
resembles chlorite than hornblende. 
Gneiss, Primrose Hill_—The specimen was selected as an example 
of one of the less obviously gneissic varieties. Under the microscope, 
however, its structure is clearly that of a metamorphic rock. As 
might be expected from the darker aspect of the specimen, it is 
poorer in quartz than the last, and has much of a chloritic mineral, 
not, i think, hornblende, though perhaps replacing it, also some de- 
composed felspar and a good deal of the epidote-like mineral named 
above, probably replacing felspar. 
Two other specimens from the N.W. side, near the top, are very 
different. One is a compact dull greenish rock of rather brecciated 
aspect, the other a cherty-looking rock of a brownish-buff tint. The 
former appears to consist of rather angular fragments of felspar, 
with some quartz of variable size, imbedded in an earthy-looking 
matrix, often dark with opacite, and with some chlorite—a rock of 
clastic origin, though considerably altered. The other is even more 
distinctly fragmental; the matrix is earthy-looking and not quite 
so dark as the other, occupying a‘larger part of theslide. The frag- 
ments, as before, are quartz and felspar ; and many of them show a 
minute graphic or fibrous structure, as exhibited in the above- 
described specimens, suggesting these as the source whence their 
materials haye been derived. 
The specimen labelled “halfway up” is a very different rock. 
It is of igneous origin, rather finely crystalline, consisting of felspar 
