Mineralogy and Petrograpny. 17 i 
rites as their equivalent terrestrial effusives. The gabbros he ac- 
knowledges to be intrusive, and would regard as the intrusive equiva- 
lents of the diabases. In recapitulating his views the author divides 
the diabasic rocks into (i) intrusives (gabbros, granitoid-diabases), 
and (2)effusives, {a) terrestrial (augite-porphyrites and melaphyres), 
and {h) sub-marine ( ophite-diabases ). The diorites he would 
separate into those which are merely altered phases of dia- 
base (including the epidiorites and the proterobases), and the pri- 
mary diorites, which owe their hornblendic constituents to the pres- 
ence of water vapor in the magma from which they solidified. Since 
hornblende is found only in those portions of rocks which cooled 
in the intratellurial period, /. e., under such pressure as w^ould pre- 
vent the escape of water, the diorites are to be looked upon as 
characteristic plutonic rocks. — The kersantite ^ dyke rocks from 
south-western East Thuringia contain numerous inclusions of gran- 
ite which have been more or or less affected by the enclosing rock. 
The quartz of the granite has been enlarged by the addition of new 
material, and has yielded tridymite as a product of its alteration. It 
contains numerous glass inclusions as the result of the fusion of 
original mica inclusions. Mica, augite and a new crystallization of 
feldspar have originated from the feldspar of the granitic rock. The 
original mica has changed into spinel and augite. Garnet, sillimanite, 
rutile, and apatite, which were among the original constituents of 
the granite can no longer be detected in the inclusion. The ground- 
mass in which the new minerals lie consists of a micro-felsitic ag- 
gregate of quartz and feldspar, in which are numerous concentric 
and radial spherulites, and a well-marked fluidal structure. Inclu- 
sions of a mica schist, and of a cordierite bearing andalusite contact 
rock are also found in the same kersantite.— Mr. Cross ^ communi- 
cates some brief descriptions of a few of the eruptive rocks occurring 
m Custer Co., Colorado. The first rock described is a garnetifer- 
ous rhyolite with a eutaxitic structure. It is remarkable for its sim- 
ple composition which is as follows: 
SiOa AI0O3 Fe^Os FeO MnO CaO MgO KoO NaoO H^O P2O5 
75-20 12.96 .37 .27 .03 .29 .12 8.38 2.02 .58 tr. = ioo.22. 
A sanidme-oligoclase-trachyte possesses the peculiarity of a second- 
ary porous structure due probably to the alteration of inclusions. 
Its biotite has yielded augite on its corroded edges. In a syenite 
occurrmg in narrow dykes are irregularly-shaped pieces of biotite, 
with their greatest development in the direction of their ^a.xes. Peri- 
dotite and an olivine-augite-diorite are also described. The former 
contams brown hornblende and hypersthene in about equal propor- 
tions. The same writer'' announces the discovery of a second oc- 
currence of phonolite in the United States. The specimen examm- 
\ R. Pohlmann: Neues Jahrb. f. Min., etc. 1888. II. p. 87. 
3 p'"''- J:*"'- '"'^"i^"'- '"^oc. 1887. p. 228. 
Proc. Col. Scent. Soc. 1887. p. 167. 
