Metamorphism of Dolerite into Hornblende-schist. 145 
deposits formed of bones, and to iron and alumina phosphates 
found in Redonda, Alta Vela, and Testigos Islands. 
4, “ Notes on Species of Phyllopora and Thamniscus from the 
Lower Silurian Rocks, near Welshpool, Wales.” By George Robert 
Vine, Esq. (Communicated by Prof. P. Martin Duncan, F.R.S., 
F.G.S.) 
January 14, 1885.—Prof. T. G. Bonney, D.Sc., LL.D., F.R.S., 
President, in the Chair. 
The following communications were read :— 
1. “The Metamorphism of Dolerite into Hornblende-schist.” 
By J. J. Harris Teall, Esq., M.A., F.G.S. 
The author referred to two dykes which occur in the neighbour- 
hood of Scourie, Sutherlandshire. Their general direction is N.W. 
and S.E.; and as the prevalent strike of the gneissic banding is, 
roughly speaking, N.E. and 8.W. (not N.W. and 8.E. as is usually 
the case with the Hebridean gneiss of Sutherland), there can be no 
doubt as to their true character. It is impossible to regard them 
as bands in the gneiss. 
The author's observations referred more particularly to the 
southern dyke, which is well exposed on the sea-shore on the north 
side of Scourie Bay, and especially at the promontory named Creag 
a’ M‘hail. The rock of this dyke occurs in two very different forms, 
which are proved by chemical analysis to agree very closely in com- 
position. The one is a typical dolerite (German “ diabase’’), the 
other a typical hornblende-schist. Transitions from one form to the 
other are easily traced. Veins of quartz and, in one case, a vein of 
nearly pure andesine were observed in the dyke. An analysis of 
the latter mineral was given in the paper. 
The original rock is composed of pyroxene, lath-shaped felspars, 
titaniferous iron-ore, frequently in skeleton rhombohedra, and apa- 
tite. ‘This may be traced by gradual stages into a massive rock, in 
which the augite has been completely replaced by green hornblende, 
and the original microstructure entirely destroyed. The modifica- 
tions in the felspar-substance have not been worked out; but the 
resulting product is frequently a colourless mineral, without any 
definite external boundaries, and often difficult to distinguish from 
quartz. In many cases the author found himself unable to decide 
whether the colourless grains occurring in the altered rock were 
quartz or felspar, or some mineral resulting from the modification 
of felspar. 
The massive rock in places passes into a typical hornblende-schist, 
and the transition may be often seen in a hand specimen. The 
schist is composed principally of crystallme grains of green horn- 
blende, a colourless mineral or minerals (quartz and telspar ?), tita- 
niferous iron-ore, sphene, and apatite. The hornblende grains show 
