Geological Society of London. 338 
rocks collected were subjected to microscopic examination. After 
summarizing the work of previous writers, the author proceeded to 
consider the hornblende schists. He described these rocks and gave 
a table showing their constituent minerals. He noted the absence 
of quartz, the presence of pyroxene, and the fact that the minerals 
present are those commonly met with in volcanic rocks either as 
original minerals or as secondary products, and he considers that the 
microscopic study of the schists confirms the opinion of some 
previous writers that the schists had a volcanic origin and consisted 
principally of ash-beds. The absence of free quartz militates 
strongly against the supposition that they were originally sedi- 
mentary rocks of an ordinary character, whilst the fact of their 
being bedded shows that they are not plutonic. The author has 
_ found no evidence that the foliation of these rocks is due to dynamic 
deformation, and gives reasons for supposing that such was not the 
case. ‘The rock seems to have been originally homogeneous, and its 
banding produced at a later stage by the segregation of the horn- 
blende in planes parallel to the bedding. 
The rocks furnish abundant evidence of the action of water, as 
shown by the presence of calcite, chlorite, steatite, and other pro- 
ducts of aqueous action, as well as by channels fringed with magne- 
tite, ferrite, or limonite. The action of water in converting augite 
into hornblende may be distinctly traced when the slices still contain 
pyroxene. The production of periodical currents of water through 
the water-bearing strata adjoining the roots of a volcano was com- 
mented on, and the author suggested that the banding of the horn- 
blende schists was produced by such water leeching out unstable 
minerals, such as pyroxene, from the spaces between the planes of 
lamination, and the formation of comparatively stable minerals, 
such as hornblende, along those planes. The Lizard rocks contain 
good examples of the formation of hornblende in the wet way, that 
mineral having been deposited in cracks in such a way as to join 
together the ends of hornblende crystals severed by these cracks. 
The “granulitic” group, of which the author gave a table 
showing the constituent minerals, was then described. Judged by 
their mineralogical contents the dark bands consist of diorite and 
the white bands of granite. 
The author considers that portions of this group consist, like the 
hornblende schists, of converted ash-beds, but that other portions 
are composed of intrusive diorites of later date, the quasi-bedded 
appearance of both being due to the injection of granite. He 
pointed out that the quasi-banding is very irregular in its 
character, that the bands inosculate, bifurcate, aud entangle them- 
selves in complicated meshes inconsistent with the idea of regular 
banding, and that they are deflected by the blocks of serpentine 
imbedded in the dioritic portions of the granulitic rocks as well as 
by the porphyritic crystals of felspar contained in the latter. In 
certain places, as on the foreshore at Kennack Cove, the intrusive 
character of the granitic veins is undoubted, as they cut through 
the diorite in all directions, but they graduate into bands of normal 
