214 
PETROLOGY OF LOCAL PEBBLES. 
Sep., 1889. 
THE PETROLOGY OF OUR LOCAL PEBBLES. 
BY T. H. WALLER, B.A., B.SC. 
(Continued from page 178.) 
(2) A white quartzite (2) from Sutton. 
The component grains are more rounded than is the case 
in (1), but still they must be called subangular. They are of 
about the same average dimensions as those in the last 
specimen, but a quartz vein cuts across the section, and in it 
the “ mosaic ” is on a good deal larger scale. 
This pebble also contains a considerable quantity of what 
appears to be a decomposed felspar; the edges of the fragments 
are only just rounded off, to no greater degree than the quartz 
grains. One grain was observed showing the cross hatched 
extinction pattern of microcline. 
A good many zircons and tourmalines of considerable 
size lie among the quartz grains, but not in them ; unless one 
crystal of which the exact form could not be distinguished, 
but which possessed a high double refraction, may have been 
a zircon. Some bodies of high refractive index, as shown by 
the solid appearance they had in the quartz, appeared isotropic, 
and seemed to have crystal faces, but the shape could not be 
made out. There is also a number of grains of a colourless, 
or very faintly yellow, mineral, apparently decomposed, along 
cracks, which stands out in decidedly greater relief than the 
quartz grains and does not appear to have the secondary 
quartz grown to it. 
(3) A yellowish white quartzite (4), from Sutton. This 
pebble contained lingula. 
The quartz grains are small, from *005 to '003 of an inch. 
They are slightly rounded, and the cementing quartz is in 
optical continuity with them. A few flakes of white mica 
and a few grains of felspar are mixed with the quartz, but 
the most noticeable feature is the verv great richness in 
zircon and rutile, especially the former. In one field of 
2 l o inch diameter I counted ten rounded grains of zircon and 
two or three of rutile. They appear to have been loose in 
the sand from which the quartzite had been compacted. 
A small quantity of this quartzite was treated with 
hydrofluoric acid, and the grains which were left collected 
by subsidence. They are, as the slide shows, zircons and a 
few rutiles. In the solution, after evaporation to get rid of 
the silica, titanic acid and zirconia could be easily detected ; 
