SOME NORTH-OF-ENGLAND DYKES. 239 
Morrrra DYke. 
Literature. 
_ Lesovr, Prof. G. A. Geology of Northumberland, p. 48. 
Ordnance Map 105 N.W. 
Specimens of this dyke have been kindly given to me by Prof. 
Lebour. It crosses the Wausbeck a few yards below the viaduct of 
the North-Eastern Railway near Morpeth (‘Geology of Northum- 
berland, p. 48). The rock is somewhat blacker and more closely 
crystalline than that of the dykes hitherto described; it is also 
denser, its specific gravity lying between 2°88 and 2°89. Crystals and 
crystalline granular aggregates of felspar (? anorthite) occur as por- 
phyritic elements; but as they do not differ markedly in size from the 
larger felspars of the ground-mass, they are not so easily recognized 
in the hand-specimen as in the thin section. 
Mr. Stead has analyzed the rock with the following result :— 
Sila yi 4 es oe 51°20 
PAULIN ae. eek Soe a ae 20:03 
Hercicxoxides 4". ee TORE 
JL ASTNG) ie as tO tg 10:52 
IMaamMeSIa 5.4 3). 6°75 
RO GASH iat cg while ce 0-51 
SOC cs aan ane ae aIAD Wer 
Wider eh cue ewes 70) 
99:99 
Under the microscope the rock is seen to have very close relations 
with that of the Tynemouth and the related dykes. There are the 
same porphyritic felspars and amygdaloids, although these are not 
nearly so abundant or so large as in the Tynemouth rock, and the 
same long lath-shaped felspar sections, irregular grains and plates of 
pyroxene, and interstitial matter, with its various devitrification- 
products. There is, however, one important point of difference: oli- 
vine, both fresh and in the form of a green and brown serpentinous 
pseudomorph, is comparatively abundant in this rock. This occur- 
rence is of some interest, on account of the rarity of this mineral 
in the rocks described in this paper ; indeed this is the only rock 
here referred to in which I have detected the mineral in an un- 
altered condition. 
Tt must not be supposed, however, that this fact. differentiates 
the Morpeth dyke from the dykes of Hebburn, Tynemouth, Brun- 
ton, Seaton, and Hartley ; for in all other points there is the closest 
resemblance between them; and, moreover, pseudomorphs after 
olivine occur sparingly in the Tynemouth and probably also in the 
other dykes. 
Hicu-Green Dyxkzs, | 
Literature. 
Lesovr, Prof.G. A. Geology of Northumberland, p. 50. 
Ordnance Map 108 S.E. 
