410 
HARKER : PETROLOGICAL NOTES. 
In some former notes I described specimens of boulders from 
the Basement Clay at Bridlington Quay and Dimlington, which I 
referred to the augite-syenites of the neighbourhood of Christiania 
(vol. xi., pp. 303, 304). Further examination and comparison with 
specimens from Frederiksvaarn, &c., [1091, 1133] leaves no doubt 
of the correctness of this determination. Since that time Mr. J. W. 
Stather has given me another specimen from Dimlington, which, 
though rather darker in aspect, agrees closely with the former, 
showing the same rather coarsely crystalline aggregate of felspai's 
and pyroxene with some flakes of lustrous brown mica. Under the 
microscope [1065] this rock shows a close resemblance to [936], 
abeady noticed. The large crystal-plates of felspar show no 
plagioclase lamellation, and only a very delicate cross-hatched 
structure when viewed between crossed Nicols. The augite shows 
a diallagic " schiller "-structure only inconstantly, and chiefly in 
the interior of the crystals. A deep brown mica is present, as 
before, often in close association with imperfect crystals of magnetite, 
while apatite prisms are enclosed by all the other constituents. 
Among Mr. Lamplugh's specimens is one, No. 543, from the 
middle of High Stacks, of a moderately coarsely crystalline rock 
showing large grey felspars, black pyroxene, and a golden-brown 
mica. A shoe of this [1139] shows characters very similar to those 
of the preceding. The felspar, in broad, irregular crystal-plates, is 
almost entirely orthoclase, with no microcline-structure, but it has 
minute opaque rod-like interpositions disposed in parallel lines. The 
pale-green augite has similar enclosures, sometimes densely grouped 
and in two sets of intersecting lines. Magnetite is rather plentiful. 
The brown mica is either associated with this, or intergi'own with the 
margins of the augite, or in minute flakes within the felspar crystals. 
These crystals also enclose minute apatite needles, often with parallel 
arrangement, and larger apatite prisms occur here and there in the 
rock. 
Although two types of Norwegian augite-syenites can be recog- 
nised in the East Yorkshire boulders, we have not yet identified any 
specimen of the associated elseolite-syenites from the same source. 
Another Norwegian type of rock represented in our collection is 
