Sep., 1889. 
PETROLOGY OF LOCAL PEBBLES. 
215 
but it did not seem worth while to undertake the very 
awkward quantitative separation of these oxides, especially as 
such a large quantity of mineral had escaped solution. 
(4) A light quartzite (18), with dark bands about inch 
wide, and at distances of from three to five-sixteenths of an 
inch. This pebble was obtained from a stoneheap by the 
roadside between Alvecurch and Blackwell, so that the exact 
place in the beds is uncertain. 
It is composed of somewhat angular quartz grains, many 
somewhat rectangular in shape, and in parts of the section 
these appear to lie with the longer dimension of the rectangle 
across the direction of the banding, so that, neglecting the 
banding which, under the microscope, is not very obtrusive, 
the impression is certainly of the bedding being at right 
angles or thereabouts to the bands. The dark bands are 
produced by black cloudy grains of quartz and by a black 
dust, which in some cases incrusts the quartz grains, and in 
others is distributed through the cementing quartz. Where 
it has incrusted the grains it has not by any means always 
prevented the optical continuity of the old and new material. 
Flakes of white mica are rare, and a few zircons are 
present as usual. 
(5) A dark red quartzite (30) from Sutton. 
The grains of quartz are subangular, and the rock owes 
its colour to the pellicle of oxide of iron with which almost 
every grain is covered. This has prevented the cementing 
quartz from being deposited on the original, and it fills the 
interspaces which, from the angular character of the com¬ 
ponent grains and the consequent close fitting, are, on the 
whole, small, in masses which show a coloured mosaic in 
polarised light, 
(6) A pebble from Sutton (24) which has the appearance 
of a coarse grit. 
It shows, however, on microscopical examination, that it 
has been subjected to very great shearing. The larger pebbles 
are crushed, and in many cases recemented with new quartz; 
and in scarcely any one of them is the polarisation uniform and 
normal, but shows the irregular shadows due to the deform¬ 
ing of the crystal. Flowing as it were round them, and 
prolonged in considerable tails and streams, lie abundant 
minute flakes of a pale mineral, of high double refraction— 
probably some form of mica. A few large zircons are 
present, and there is a very large development of new 
quartz in the interlocking grains which characterise the 
schists, but on a small scale. 
