W. M. Hutchings—Ottrelite in North Cornwall. 219 
needles of rutile. In the course of an investigation of the ilmenite 
and leucoxene of certain schists from Wildschonau in the Tyrol 
(Zeitschrift fiir Krystallographie u. Mineralogie, Band 6, pp. 244— 
256) he found that ilmenite, which was perfectly homogeneous and 
opaque under the microscope, left a considerable amount of such 
residue on solution. By using hydrochloric acid for this purpose, 
he was able to detect combinations of the most delicate needles of 
rutile in networks and “gratings ” of sagenite. 
He does not say whether he himself came to any conclusion as to 
the primary or secondary nature of these interpositions, which 
appear to correspond with what is so well seen in the thin ilmenite 
flakes of the Cornish slate; neither does Rénard, so far as I am 
aware, express any opinion on this point, nor do I know of any 
other authority who has done so. 
After long and careful examination of these forms I do not find it 
possible to say that there is much evidence one way or other, but 
consider that on the whole it appears most probable that it is a case 
of original inter-crystallization. 
The study, under high powers, of the thinnest, most transparent 
flakes in every degree of reticulation, seems to show that in all cases 
the rutile of the sagenite is so very sharply marked off from the 
ilmenite that the idea of a chemical change going on between the 
two is not easily entertained. 
The whole question as to the mode of origin of these ilmenite 
flakes is one of great interest. It seems clear, from the manner of 
occurrence in the rock, that like the ottrelite they were produced at 
some period posterior to the formation of the sericite-phyllite as 
such, and there is much evidence that they also have been much 
torn and broken up at a still later period. 
Calcite is present in this slate in noticeable amount in the form of 
grains and small patches irregularly diffused all through it. 
There are a few small patches of pale chlorite, of which it is to 
be remarked that they are quite free from the microlites of rutile, so 
abundant in the rest of the rock. Tourmaline in perfect hemihedral 
crystals is well represented, these crystals measuring in most cases 
soo inch in length. They appear all to lie with their long axes 
parallel to the plane of cleavage of the slate. 
This slate is so completely metamorphosed that nothing whatever 
can be detected which could be referred to the original clastic 
material out of which it has been formed, except a few crystals and 
rounded grains of zircon. 
Roofing-slates from other quarries of the district all resemble that 
just described in general structure and composition, though, with the 
exception of the fundamental basis of sericite, the amounts of the 
various minerals present vary a good deal. Thus ilmenite is much 
more abundant in some than in others, and in some cases does not 
show any sagenite. The latter is present in numerous and fine 
examples, however, in the Delabole slates. 
Garnets are plentiful in some slates, as at Delabole. 
The other phyllites, not fit for roofing-slates, show rather more 
