W. A. Richardson—A Basic Dyke at Charnwood. 173 
The dyke-rock b has the characteristics already described for the 
marginal phase, but the felspar laths show fluxion arrangement 
parallel to the line of contact. 
The porphyroid at the contact has in hand-specimens quite a 
different appearance to the normal rock. In colour it is generally 
lighter, greenish, and blotchy. The normal dark-coloured rock 
can, however, be found attached to fresher portions of the dyke. 
I think that Professor Bonney is correct in considering these colour 
variations in the porphyroid as due to weathering, for here the two 
rocks have often parted along the contact line, and so afforded a 
passage for water. 
Fic. 1.—Junction of Peldar Tor porphyroid (c) and dolerite dyke (6). x 54. 
Under the microscope the porphyroid, c, Fig. 1, has the same 
general appearance as in the normal rock. There is, however, a 
marked absence both of traces of ferromagnesian minerals and 
epidote. Instead there is a large amount of indeterminate green 
material in the groundmass. The felspars are sometimes distinctly 
resorbed, and the groundmass near the contact has recrystallized. 
It then consists of rounded grains of what I take to be felspar set 
in a felted network of the greenish material already mentioned. 
Small lenticular patches, e, Fig. 1, of clear recrystallized material 
are caught up along the line of contact, and suggest a certain amount 
of marginal assimilation by the dyke. Along the contact line in one 
