41 (j HARKKK : PPTROLOGICAL NOTES. 
be the most abundant constituents. Some are deeply altered, with 
numerous secondary products ; others have the limpid appearance 
usually seen in the re-crystallised felspars of highly metamorphosed 
rocks. Some crystals have fine twin-lamellation on the albite type, j 
occasionally crossed by a second set of lamellae (the pericline twin- 
ning) ; others, without twin-lamellation, show between crossed 
Nicols a finely veined structure. Fissures in the crystals are j 
sometimes occupied by veins of crystalline calcite ; elsewhere 
granular, brilliantly polarising epidote occurs, often in strings 
following the twin-lamellse, which are known to correspond to 
planes of chemical weakness, but also usurping, together with 
quartz, the whole of an area formerly filled by felspar. Granules 
of epidote and patches of well-cleaved crystaUine calcite occur 
in the general ground of the rock, besides grains of iron-oxide, ^ 
and a pale-green dichroic mineral of the chlorite family in bent j 
flakes, giving rather low polarisation-tints. What appears to be ] 
a single rounded gi-ain of quartz is sometimes found, when examined ^ 
in polarised light, to consist of a crystaUine mosaic of clear, irregularly- ] 
shaped grains, and similar indications of recrystallisation are seen in 
some of the felspars. 
The rock may be regarded, then, as a very felspathic grit, almost 
an arkose, highly metamorphosed. The only possible English source . 
is the alteration-zone around the Shap Fell gTanite, where somewhat \ 
similar rocks occur. I can find no account of such a type in | 
Scandinavia, but it might probably be matched among the various \ 
metamorphosed grits of the central Scottish Highlands, if we admit ; 
the possibility of rocks being transported from that region to our i 
coast. It is a priori probable that the well-known Shap granite | 
boulders should be accompanied by specimens of the altered rocks, 
at least equally durable, which surround the granite outcrop, and I • 
have already suggested such an origin for another of the Flamborough ^ 
boulders . ' 
I pass on to a specimen from the beach east of South Sea ' 
Landing. This is one of the so-called " porphyrites," and closer \ 
examination shows it to be a partly decomposed hypersthene- ^. 
andesite. It has a brick-red ground-mass enclosing striated felspar 
