of Edinburgh, Session 1881-82. 
669 
composed of quartz grains, of which some are milky, and a good many 
are covered with hydrate of iron. Associated with the quartz are 
many black particles of hornblende, mica, magnetite, and yellow- and 
— ante-tertiary, the second (II.) those of recent rocks — tertiary and post-tertiary. 
We only mention those minerals which are found in the deposits. 
I. 
Quartz — containing many liquid en- 
closures. 
Orthoclase — without inclusions or rare 
liquid inclusions, dull aspect, 
and milky colour, crystals tabu- 
lar and thick, Carlsbad twins. 
Microcline. 
Plagioclasc — in general aspect dull, 
decomposed in micaceous sub- 
stance into epidote, in pinitoide, 
in fibro-radiate zeolithic matter, 
in quartz, in calcite. 
Pyroxene— enstatite, bronzite, dial- 
lage and augite, the latter very 
often decomposed, transformed 
into ouralite. 
Amphibole — greenish colour, often de- 
composed into epidote, &c., asso- 
ciated with quartz and calcite ; 
fibrous forms, extremely irregular 
(Hyperstliene). 
Muscovite. 
Wanting. 
Wanting. 
Wanting. 
Tourmaline. 
Anatase, Rutile , BrooTcite. 
Cordierite. 
II. 
Quartz — containing vitreous enclo- 
sures. 
Sanidine — many vitreous and gaseous 
inclusions, aspect vitreous and 
brilliant, structure zonary, charac- 
teristic cracks independent of the 
cleavage ; cleavage following 
coP oo. Baveno twins. 
Wanting. 
Plagioclasc — (Microtine), aspect vitre- 
ous, in general decomposition less 
advanced in the Microtine than in 
the plagioclases of ancient rocks ; 
vitreous and gaseous enclosures 
more frequent and better marked ; 
enclosures of associated minerals, 
&c. 
Pyroxene — especially augite, slightly 
decomposed ; numerous vitreous 
enclosures, especially in the augites 
of basalts, zonary. 
Ampldbole — deep brownish tint, gene- 
rally with crystallographic con- 
tours more marked, zones of dif- 
ferent colours, sections surrounded 
with magnetite, compact, numer- 
ous inclusions. 
Wanting or secondary. 
Trydimite. 
Leucite. 
Nosean and Hauyne. 
Zeolithcs. 
Wanting. 
Wanting. 
Extremely rare. 
It is scarcely necessary to mention that all the foregoing refers only to 
massive crystalline rocks, and when the minerals are in an isolated state we 
cannot always say whether they come directly from these rocks, or from the 
disintegration of sedimentary layers, or from schisto-crystalline rocks. These 
latter frequently occur in the deposits. In these questions we have always 
taken into consideration the lithological associations and the geographical 
position of the deposit. J. M. and A. K. 
