174 W. A, Richardson—A Basic Dyke at Charnwood. 
slide there is a green mineral, with the refractive index and 
pleochroism of hornblende, but a low extinction. More exact 
determination is difficult, for there are only two or three small 
pieces all similarly orientated. Whether this is the product of 
contact metamorphism, or is developed by the crushing of the mass, 
is difficult to say. 
d vA VA \A\ A Face 
y in Vey, V7 
Jy XA ; i We 
/ ys y, MA VA iy 
Loe NN 
Ve A Wy 
a \o Vg) 7 \Z% 
an 4 vA iF % DG 
Ne Gouat 7, Vr 'Efoor 
me Zn 
/ VA 
MENA YD 
eS) 
Qa. 
Ss 
Mp AG 
YG ya 
PA Z 
Fic. 2.—Diagrammatic plan of quarry floor showing the form of the laminated 
marginal sheets. Hatched portion=porphyroid, blank=dolerite dyke. 
Ill. Fir~tp RELATIons. 
The most interesting features of the dyke are to be found in the 
field. 
The dyke trends W.N.W. and hades to the east at about 
5 degrees. Its width varies somewhat; but is nowhere Jess than 
12 feet. 
Professor Bonney thinks that it has suffered more than the 
porphyroid from shearing. Specimens from the margin do cleave 
much more readily than the latter rock, but this is doubtless due in 
part to the fluxion banding already mentioned. The dyke at the 
