THE WARWICKSHIRE COAL-FIELD. 641 
view there is, of course, the difficulty of an easily decomposed 
mineral like nepheline having remained unaltered from Paleozoic 
times ; but, on the other hand, it should be remembered that olivine 
presents a similar difficulty, yet has nevertheless been frequently 
preserved unchanged throughout the same enormous periods. 
Two of the secondary constituents have already been mentioned, 
namely calcite and viridite, or a serpentinous substance ; to these 
may be added an orthorhombic zeclite which fills small cavities with 
long radiated lamellar crystals; they are clear and colourless, but 
exhibit brilliant colours in polarized light. 
Quarry close to Atherstone.—In this mass the hornblende is also 
accompanied by a considerable quantity of very pale brown augite ; 
the crystals are-well formed and among them are several twins. 
The felspar is highly altered, but a few crystals may be recognized 
as triclinic. In two slices examined there were no pseudomorphs 
after olivine. 
Railway-cutting, Chilvers Coton.—This is an excellent locality 
for collecting well-marked varieties of the intrusive rocks. On the 
west side there is a light-coloured mass composed chiefly of pink 
felspar, with rather long prisms of altered hornblende scattered 
through it. Another variety is of a dark green colour, and consists 
almost entirely of hornblende in comparatively large crystals. 
Between these extremes there may be found several intermediate 
varieties. Microscopic examination of these rocks affords no addi- 
tional fact of importance. 
ConcLuUsIon. 
It appears from the preceding investigation that the intrusive 
rocks of the Warwickshire coal-field are for the most part ordinary 
diorites, but that they also occasionally present remarkable variations 
from the normal type. 
The varieties described appear, however, to be strictly local ; and 
in all of them the predominant and characteristic constituents are 
a triclinic felspar and hornblende, together with a little magnetite and 
apatite ; a glassy or felsitic matrix is also nearly always present. 
Hornblendic rocks containing augite and olivine have not been 
previously found in these islands, nor, I believe, elsewhere, except 
among rocks of Tertiary or later age. They appear, moreover, to be 
rather rare everywhere, a few only having been observed among the 
hornblende and augite andesites* or the Bohemian basalts described 
by Boricky f. 
It is now certain that rocks of precisely similar composition were 
erupted during the later Paleozoic period ; how much earlier remains 
to be seen. The existence of these rocks may therefore be regarded 
as additional evidence against the singular notion, apparently held by 
many, that the products of volcanic action were in some unaccount- 
* Zirkel, Lehrbuch der Petrographie, vol. ii. p. 222. 
+ Basaltgesteine Bohmens, pp. 137, 138. 
