238 
PETROLOGY OF LOCAL PEBBLES. 
Oct.. 1889. 
(17) A pebble (No. 37) from Sutton has porphyritic 
crystals of felspar almost perfectly fresh and transparent, 
and quartz containing in places beautiful glass cavities, with 
a bubble in each. The ground mass of the rock is splierulitic, 
passing in places into a micro-pegmatite of a clear mineral, 
which we may take to be quartz, and a dirty-looking sub¬ 
stance, which probably represents felspar. 
(18) In another pebble (21) from Blackroot Pool, Sutton, 
the appearance is such as we might imagine to be produced 
by the crushing and rolling out of such a rock as the last. 
The quartz grains are broken up into lines and strings, which 
have been recemented into continuous masses again, and the 
total aspect might almost be described as that of a gneissose 
felsite. That such has been the mechanical origin of the 
rock I do not, however, feel sure. The quartz contains many 
more fluid cavities, but they might be secondary. At the 
edge of some of the quartz the ground mass runs into it in 
a very peculiar manner, almost like the teeth of a comb, and 
a place or two exhibits a very fine cross striation in the 
arrangement of the components. 
(19) By far the most curious specimen is from Catspool 
(No. 39). It has a somewhat gneissic look in the hand 
specimen, but without any very determinable foliation as to 
minerals. A thin section with a low power has a most 
wonderful similarity of aspect to a section of wood; the 
general lamination in the one direction being crossed bv 
groups of browner parts almost at right angles. When 
examined with crossed nicols, the whole breaks up into 
areas of considerable size, which however do not polarise 
uniformly, but are subdivided again. All one of the larger 
areas may be on the whole dark, but the smaller portions 
which make obvious the longitudinal grain, so to speak, of 
the specimen may have various degrees of shading. ' No 
quartz is visible, the whole has very much the general look 
of a felspar which has been crushed out of shape. 
Four specimens are exactly of the Wrekin type. 
(20) One from Catspool (20) is exactly similar to the pale 
brown, finely flow-banded rock of the Wrekin itself. 
(21) Another (13) from King’s Heath is splierulitic, but 
not in very good condition ; while 
(22) A third (10) from King’s Heath is precisely of the 
type of the splendid Lea rock specimens, but bleached to a 
pale yellow brown. 
It presents the same spherulites with central quartz masses, 
often also with similar agate linings, the same microlitlis, and 
in a striking degree the very beautiful perlitic structure. 
