Sep., 1889. 
PETROLOGY OF LOCAL PEBBLES. 
217 
I may also refer to Mr. Teall’s report on the subject in 
the paper of Mr. Harrison’s previously quoted. 
The next group of specimens derived from the pebbles to 
which I will call your attention is a remarkable set of 
tourmaline-bearing rocks. 
They vary from pebbles consisting of pure white quartz, 
pierced by needles of tourmaline of the black variety, of quite 
considerable dimensions, such as No. 6, to others where the 
mixture of the minerals is more uniform, such as No. 48, from 
Sidnal Farm, Blackwell, and No. 25 from Sutton, and further 
to such a perfect schorl schist as No. 5, which I owe to the 
kindness of Mr. A.T. Evans, who collected it at the King’s 
Heath pit. With these we find specimens at Alvechurch, 
Moseley, and Sutton, of a sort of breccia, Nos. 7 and 8, in 
which the component fragments are of a sort of schorl schist, 
and the cementing material contains also a very large 
quantity of the tourmaline. 
In addition to these we find at King’s Heath pebbles of a 
porphyritic granite and of an elvan in which a large amount 
of tourmaline is contained. In the latter rock it would 
appear from the forms of the tourmaline aggregates that they 
replace, in some instances at all events, crystals of felspar. 
To take a few of these in more detail. 
(9) Quartz-tourmaline rock from Sidnal’s farm, Blackwell. 
A coarse grained mixture of the two minerals. The 
quartz is clear and polarises in large areas. There are a 
considerable number of fluid cavities, but none containing 
salt crystals were observed. 
The tourmaline belongs largely to the variety which, in 
certain directions, possesses the splendid blue colour, in 
consequence of which the name indicolite has been given to 
it. As is usual, patches and blotches are differently coloured 
in the sections, and, except in basal sections, which in several 
cases are quite hexagonal, there is presented the striking 
dichroism peculiar to tourmaline. Clustered on the edges of 
the larger masses are fringes composed of fine blades of the 
same mineral, with the same blue and yellow colours. These 
fringes are at times of considerable length, i.e., of about 
of an inch. It forms an object of great beauty for a low power. 
(10) A dark rock (25) from Sutton. 
This has the appearance of a dark quartzite, but a thin 
slice shows that it is really a very similar rock to the last, 
but of finer grain. It is, also, distinctly schistose, the 
tourmaline forming more or less connected ramifying strings, 
made up of very minute grains winding among grains of 
quartz. 
