242 J.J. H. TEALL—PETROLOGICAL NOTES ON 
but more frequently as crystalline granular aggregates. It appears, 
in the thin section, of a pale brown colour. Twinning is common, 
and the prismatic cleavages are usually well marked. The lath- 
shaped sections frequently interpenetrate the pyroxene, thus giving 
rise to the diabasic structure. 
Ilmenite.—This occurs in large opaque plates of great irregularity, 
interpenetrated by the other crystalline elements. The habit of 
this mineral in the High-Green rock is exactly the same as in the 
diabases of the Hartz, Nassau, and Saxony, except that it is not 
altered into the white silico-titanate of lime. 
The most important secondary product is a greenish serpentinous 
mineral containing specks and veins of opacite. This may possibly 
be a pseudomorph after olivine. 
Rather more than a mile to the north of the dyke just described 
is another having a somewhat similar character. It is well exposed 
in an old quarry on the east side of the Tarret Burn, where it is 20 
or 30 feet wide, and weathers in a markedly spheroidal manner. 
‘The rock is black in colour and distinctly crystalline in texture. 
Porphyritic elements are not distinctly recognizable by the naked 
eye; but under the microscope two generations of felspar are at 
once seen to be present. 
The original constituents are felspar, pyroxene, ilmenite, apatite, 
and possibly also olivine. A very small quantity of a pale brown 
isotropic glass is present. If we except the earlier generation of 
felspars and the small quantity of isotropic glass, then there is the 
closest resemblance between this rock and that of the more southern 
dyke. ‘The other constituents have the same individual character- 
istics and are similarly related to each other ; they do not therefore 
eall for any special description. 
The felspars which give the porphyritic character to the rocks are 
few in number, and may be distinguished from the others by their 
form and by the presence of a large number of irregular ramifying 
inclusions of the ground-mass. ‘The specific gravity of the rock is 
2°92. 
Acxtineton Dyke. 
Laterature. 
Lesour, Prof. G. A. Geology ef Northumberland, p. 49. 
Ordnance Maps 109 8.W. and 108 N.E. 
The course of this dyke is thus described by Prof. Lebour :—* It 
stretches across the entire width of the country from the coast at 
Boudicar, near Acklington, cutting through Coal-measures, Millstone 
Grit, the whole of the Bernicians, the Tuedians, and the Cheviot 
porphyrites, 12... .: it runs on for many miles across the south of 
Scotland. It is well seen at numberless places along its course, 
notably at Debdon, Cartington Castle, and the road along the 
Coquet, near Shillmoor. At Acklington it is 30 feet wide.” 
I have examined it myself at the point where it crosses the Coquet, 
half a mile above the Mill, near Acklington Park, and again at two 
