420 HARKER : PETROLOGICAL NOTES. ] 
■ I 
The next specimen, No. 54, has a mottled black and light-grey \ 
appearance, due to the admixture of augite and felspar. Under the ' 
microscope [1050] the bulk of the rock is seen to consist of these j 
two minerals. The augite is very pale in section : it occurs in ,i 
twinned crystals, and, in addition to the usual prismatic cleavage, ; 
has a very delicate striated structure. There are also some fibrous ' 
dirty-green pseudomorphs after a rhombic pyroxene. A few flakes \ 
of brown mica occur, besides irregular crystal-grains of magnetite, 1 
and rarely one or two needles of apatite. The felspar is chiefly in 
little elongated twinned crystals, with a few larger ones, and a zonary 1 
shading is often seen in polarised light. A little quartz, occurring ■ 
interstitially, is the latest product of consolidation in the rock. | 
There is no doubt that we have here a specimen of the Whin Sill j 
of Teesdale, described by Mr. Teall. Our rock agrees identically ■ 
with specimens taken at High Force [378, 379]. J 
No. 167 is a rock of slightly coarser grain, the ophitic arrange- ^ 
ment of part of the pyroxene being easily seen. Its microscopic ! 
structure is of the diabasic rather than the true doleritic type 
[1142], the division of the felspar into two generations not being 
very marked, though there are a few rather clear shapeless felspars , 
of late formation and with zonary banding. The rock is considerably i 
decomposed, but retains evidence of having contained both mono- 
cHnic and rhombic pyroxenes. As before, there is clear quartz, some 
of which seems to be original ; and scattered needles of apatite occur ! 
in places in the slice. This is a specimen of the coarser variety of the | 
Whin Sill, and is no doubt from Teesdale, the outcrops to the west ^ 
of the Penines being of a finer-grained variety. 
A boulder between High Stacks and South Sea is another 
example of the coarser type of Whin Sill from Teesdale, and, as is | 
often the case, shows a little dark mica as well as augite. The | 
rock is considerably decomposed, and contains specks of iron pyrites. | 
Its microscopical characters [1058] do not need detailed description, 
since they agree generally with the foregoing. The augite here is I 
yellowish-brown in section, and usually twinned ; it shows the basal ^ 
striation already mentioned very markedly. 
Another sliced specimen [1057] is a fine-grained doleritic variety, | 
