MARKER : PETROLOGICAL NOTES. 
305 
fifth of ail inch in length and with partial parallel arrangement, and 
rounded grey spots of quartz. It may be styled hornblende-gneiss. 
Micro. The hornblende sections are greenish-brown or dull- 
green, with strong pleochroism, vibrations parallel to the axis of 
greatest absorption (which is inclined only 4° or 5° to the long axis 
of the crystal) giving a deep green tint. The crystals are of irregular 
outline, and enclpse quartz grains at the margin. The bulk of the 
slice consists of quartz and altered felspar. The latter presents a 
finely-granulated appearance, recalling the so-called " saussurite," 
and chlorite and scaly white mica are closely associated with it. The 
larger quartz-grains have, between crossed Nicols, the shadouy aspect 
due to internal strain, and they pass at the margin into irregular 
areas of granular quartz-mosaic. 'All these appearances indicate the 
action of great mechanical stresses, and the rock must have formed 
part of an area of metamorphosed crystalline rocks, such as that of 
the Scottish Highlands or Norway. 
[939] From the Basement Clay near Flamborough North Land- 
ing. A mottled dull greyisli-green and white rock, in which (piartz, 
felspar, etc., may be detected by the eye. 
Micro. This specimen again gives unmistakable evidence of 
great stresses having operated in the massif from which it was 
derived. It must have been originally a biotite-gTanite, and has been 
much altered, though without receiving a gneissic or schistose 
character. The quartz which builds much of the slice is in patches 
of granular mosaic, traversed by innumerable rows of fluid-pores, 
which have a parallel disposition, and traverse all the granules un- 
interruptedly. This is no doubt an effect of the stress. The out- 
lines of the felspar crystals are partly preserved, but their substance 
is entirely replaced by secondary products, including chlorite and 
quartz. The dark mica has also perished almost completely. 
Gneissic and similar rocks do not occur in situ in the North of 
England. Doubtless the last three specimens might be matched in 
the Highlands of Scotland, but it is impossible to assert that that is 
the home of these particular boulders, and Norway seems more 
probable. 
[940] From the Basement Clay at Bridlington Quay. A finely- 
granular, pink, felspathic rock. 
