302 
IIARKER : PETROLOGICAL NOTES. 
mineral first consolidated is magnetite, which is abundant in rude 
octahedra. Then follows olivine in rather rounded irregular crystal- 
line grains, partially conv^erted, ititp gj*;*?^ -green serpentine with 
separation of magnetite dust. The lath-slijvf)^! fslspars show albite, 
and sometimes Carlsbad-twinning, and appear to be of a basic variety. 
A minor portion of the felspar is of less basic character ; this is of 
rather later consolidation, and so in less perfect crystals, and it has a 
zonary structure. The occurrence of these two generations of felspar 
links the rock with the dolerites rather than the diabases. The 
augite, brown in section, is in plates moulding round the dominant 
felspar and other earlier minerals. 
[933] From the Basement Clay near Flamborough North Lauding. 
A basalt exhibiting green spots of olivine, black crystals of augite, 
and little shining needles of felspar in a dark ground. 
Micro. The olivine is in rather large crystalline grains, for the 
most part fresh, but locally converted into gTass-gi-een serpentine. 
The augite is in well-formed crystals of a purjjlish-brown colour with 
marked pleochroism. In ordinary light it shows a zonary structure, 
the margin of each crystal being much more deeply coloured than 
the interior. The felspar is in elongated (lath-shaped) crystals with 
fine albite-twinning and the extinction-angles proper to labradorite. 
A few felspar crystals of later formation are less perfectly built: these 
have a blurred zonary shading when viewed between crossed Xicols, 
and are probably near andesine in composition. The gTOund-mass of 
this rock is isotropic, and seems to be composed more or less of 
glassy matter. Probably none of these doleritic and basaltic rocks 
are of sufficiently marked types for the precise localities to be 
identified. It can only be said that they do not resemble either the 
Whin Sill or any of the known d3d^es of Northumberland and Dur- 
ham, but that they might probably all be matched in Southern and 
Western Scotland. 
[934] From the Basement Clay at Bridlington Quay. The 
specimen shows a dull brown gi-ound-mass enclosing partially destroyed 
felspars up to lialf-an-inch in length. They have irregular quadri- 
lateral outlines, and the interior is largely occupied by a dark brown 
material. 
