62 General Notes. 
over augite in eleolite-syenites. In it are many little veins 
of a finer-grained elmolite-syenite, which show very clearly 
the effects of pressure, and which are remarkable for the 
number of accessory minerals they contain. A second variety 
of the rock, found as blocks in the Rio de Ouro, consists of 
elxolite, orthoclase, egirine and mica, together with a large 
number of accessory constituents. Among the latter are rinkite 
and lavenite. The former’ occurs in long narrow plates, 
marked by cleavage lines parallel to their longer axes, The min- 
eral is slightly pleochroic in yellow tints. The plane of its optical 
axes is perpendicular to the cleavage. It is readily attacked by 
concentrated hydrochloric acid, with the separation of gelatinous 
silica, The lavenite? occurs in highly refractive, strongly pleochroic, 
honey-yellow crystals, and is closely associated with the magnesium- 
iron constituents. A third variety of the Eleolite-syenite is porphy- 
ritically developed. It occurs in the form of a dyke in the holoerys- 
talline rock described above, and contains inclusions of a finer-grained 
rock: of the same general nature-—The massive rocks of the Lead- 
ville Region, according to Mr. W. Cross,? comprise quartz porphy- 
ries, rhyolites, audesites, porphyrites and diorites. e porphyries 
are the most interesting, in consequence of their relation to the ore 
bodies. They are divided by Mr. Cross into several varieties, each 
of which is carefully described. That phase known as the Lincoln 
rphyry is noteworthy, as containing the rare accessory allanite.' 
he sanidines of some of the rhyolites possess a peculiar satiny lus- 
tre, due to fine partings parallel to 42 Pz. The cavities of these 
rocks are covered with little crystals of sanidine, quartz, biotite and 
topaz. In the porphyrites biotite is frequently found in tiny green 
flakes, with a very strong pleochroism, and rounded grains of quartz 
are sometimes surrounded by an aureole of quartz and feldspar. It 
is interesting to note that in certain cases epidote is the final prod- 
uct of alteration of all the minerals of the porphyrites, while in 
other cases this final product is muscovite——J. F. Williams* has 
recently described, in a very finely illustrated paper, the trachytes 
composing Monte Amiata, in Tuscany. These trachytes by altera- 
tion yield products which approach very closely to rhyolite on the 
one hand, and on the other appear very like andesites. The paper 
is enriched by numerous analyses of feldspar, hypersthene, and 
types of trachyte.-—In a late number of the Neues Jahrbuch fur 
Mineralogie, Reusch® illustrates, in a very beautiful manner, the 
effects of pressure on sedimentary and massive rocks, In the case 
of conglomerates, he shows how a schistose structure may be induc 
which is entirely distinct from the bedding due to sedimentation. 
1Cf. American Naturalist, 1884, p. 1141. 
p. 850 
3 Monog. U. S. Geol. Survey, xii., Washington. p. 319. 
1 Cf. American Naturalist, 1885, p. 1098. 
5 Neues Jahrb. f. Min., ete., Beil. Bd. v., 1887, p. 381. 
* Ib., v., 1887, p. 52. 
] 
