396 Alfred Harker— Eyes”? of Pyrites in Slate. 
the Portlandian of the Boulonnais, has convinced the present writer 
that the last-mentioned name must also share the same fate. 
Rhinobatus Bugesiacus thus occurs in the Lower Kimmeridgian of 
Bavaria and §.E. France and in the Lower Portlandian of N.E. 
France: in the first and last localities it attains its maximum dimen- 
sions, while in the second it is comparatively dwarfed. The same 
species may also perhaps be met with in the English Kimmeridgian, 
but as only detached vertebre have hitherto been discovered, it is 
at present impossible to arrive at a specific determination. 
Woopwarpian Muszum Nores. 
V.—On “Eyres” or Pyrites anp orHerR Minerans IN Snare. 
By Atrrep Harker, M.A., F.G.S. 
eee instances of the bodily deformation of rocks by lateral 
pressure, the case of the phyllade aimantifére of Monthermé is 
well known. By its strong cleavage this rock gives evidence of 
considerable lateral compression. Professor Renard? has shown 
_ that prior to this compression the magnetite crystals already existed 
in the rock, and were surrounded by a coating of chlorite. The 
crystals yielded to the pressure much less readily than their matrix, 
and the latter, having already a firm consistence, became separated 
from the crystals, carrying the chlorite with it, and was displaced 
along the planes which are now cleavage-planes, that is, in a direc- 
tion at right angles to that of the pressure. 
My object is to show that similar phenomena are not uncommon 
among cleaved rocks in our own country. Some years ago I 
obtained from the Penrhyn quarry a specimen of slate with cubes 
of pyrites, in which the displacement of the matrix around the 
imbedded crystals is well exhibited. As in ihe French phyllade, 
the vacant spaces left have been subsequently filled by infiltered 
quartz, which grew roughly perpendicular to the faces of the crystals. 
The arrangement is represented in figure 1 (p. 8397). As the “eyes ” 
are from half an inch to an inch in length, the pyrites, quartz, and 
chloritic mineral can be easily distinguished with the naked eye, 
while a thin section makes a pretty object under the microscope 
(No. 501). In the phyllade aimantifére the magnetite crystals are 
only 0:2 to 0:8 mm. in length (No. 502). M. Reusch® has noticed 
a precisely similar disposition of quartz and chlorite around dodeca- 
hedra of pyrites in a schistose diabase dyke: here too the crystals 
appear to be only about one-hundredth of an inch in diameter. 
The phenomenon is probably one of wide occurrence. It is seen 
in sericitic slates at Blaenau Ffestiniog and at other places in North 
and South Wales; also in the very pyritiferous slates of Balla- 
chulish near Oban, The “eyes” are always flattened parallel to 
’ Catal. Foss. Fishes, Brit. Mus. pt. 1, p. 83. 
* Bull. Mus. Roy. Hist. Nat. Belg. vol. ii. p. 134, and plate vi. 1883. See also 
Gosselet’s “ L’Ardenne,’’ p. 61 and fig. 17, 1888. 
* Bémmeléen og Karméen, pp. 69, 70, 1888. 
