391 
on account of their immobility and I have not, so far, 
been able to observe any really distinct changes in their 
position. Various granular ard crystalline-foliated minerals 
could not likewise be defined to satisfaction. Very fine, 
needle-like crystals occasionally occur, and they may, in 
all probability, hereafter be recognised as Avpatite, which 
would explain the presence of phosphoric acid as shown 
by the analysis, which acid has not been found in any other 
form in the rock. The aggregations of iron-pyrites exhibit 
in the thicker slides under the microscope some very interest- 
ing features, as one is enabled to recognise cubes from 0°05 
to 0.15 min. in length, edgewise. These crystals are some- 
times enclosed for over half their length in quartz crystals, 
the remaining half being embedded in the basic Topaz. 
Other very peculiar features are also observable with some 
very long fibrous forms, measuring from to 0-1 mm. in 
width by 0.3 to 0.7 m.m. in length, also partly or wholly 
encrusted by a very thin coating of Calcite. These are 
very probably lengthened cubes, which have, by some occult 
means or another, developed in one direction more than in 
another. These cubes are irregularly formed crystals of iron 
pyrites, Besides these, there also occur rectangular, nearly 
cubical, but otherwise irregular crystals of iron pyrites, 
measuring from 0°35 to 2 mm. in size; impregnated as they 
are sometimes by crystals of quartz and Calcites ; these latter 
predominate sometimes to such a degree over those sulphurets, 
which however retain their crystalline form, as to make same 
quite subordinate so far as proportions or percentage are 
concerned. 
The Calcites occupy various forms and positions within 
these iron pyrites, and they are confined sometimes by 
peculiar minute botryoidal and oblong crystals, brownish 
red in colour, which, from their general appearance, their 
distinct pleochroism, and the absence of the former fibrous 
forms, and being accompanied by a very vivid rainbow-like 
polarism, cannot be mistaken for any other but “ Titanite.” 
The Calcites of this rock, so easily distinguished by their 
vivid iridescent properties, occur most frequently in the form 
of impregnations of the iron sulphides, also in distinct, but 
smaller particles. These crystals of quartz and iron pyrites 
are evidently of a remoter origin than the basic mass of Topaz. 
Could it be assumed, for instance, that the latter consisted, 
whilst in the course of formation, or partook of the gelatinous 
compound ? 
2. Dense WuiteE Topaz or Mr. BiscHorr. 
This rock exhibits in its peculiar uneven and splintery 
fractures a trace crystalline. 
