IIARKER : PETROLOGICAL NOTES. 301 
often shows the characteristic cleavage of crystalline calcite ; but in 
other places are little ellipsoidal concretions with both concen- 
tric and radial structures, and showing the black cross in polarized 
light. Though less coarse than the usual type, there can be no doubt 
that this rock is the " Brockram," which forms the basement of the 
Permians in the Eden Valley. A slide [514] from near Appleby 
shows precisely the same characters, including the little oolitic con- 
cretions. Brockram boulders were long ago recorded by Phillips 
from the Yorkshire coast, where they are not at all uncommon. 
[930] From the Basement Clay at Bridlington Quay. A dark 
grey doleritic rock, showing little glistening felspars in a dark 
compact ground-mass. 
Micro. The porphyritic felspars, about one-eighth of an inch 
long , are rather rounded, as if by corrosion, and sometimes enclose 
l^ortions of the ground-mass. They are very clear, and show^ Carls- 
bad-twinning, but the finer twin-lamellation is very difficult to detect. 
This is owing to the nearly straight extinction of the crystals, 
which must belong to a variety of the oligoclase-andesine series. 
Augite occurs in rather smaller crystals with good forms and a 
greenish colour. These minerals, with a few rather rounded magne- 
tite crystals and rare prisms of apatite and flakes of biotite, are 
imbedded in a fine ground of decomposed felspars with magnetite 
granules. 
[931] From the Basement Clay at Bridlington Quay. A very 
fine-grained dark dolerite, showing under a lens minute needles of 
felspar. 
Micro. The felspar is mostly in bundles of " lath-shaped" 
prisms, with albite-twinning and extinction-angles suggesting labra- 
dorite ; but there is some later felspar with a rather interstitial 
arrangement and exhibiting zonary shading between crossed Xicols. 
The augite, in light-brown granules, moulds the dominant felspar, 
while the magnetite grains are slightly posterior to the augite. 
[932] From the Basement Clay at Bridlington Quay. Another 
rock of compact appearance, showing only minute narrow prisms of 
felspar scattered through a black ground. 
Micro. The specimen is found to be an oHvine-dolerite. The 
