364 Reviews—Professor Rosenbusch’s T0th Birthday. 
Fairfield. Prof. Hobbs concludes ‘‘that the generally rare gabbro, 
norite, peridotite, and pyroxenite types which most nearly correspond 
to the original ‘Cortlandt Series’ belong to a single magma which 
has here been intruded along the mutual borders of areas of granite, 
grano-diorite, and diorite, which may themselves have mingled to 
some extent ; and that it has itself been later mtruded by a fine- 
grained diorite. The extreme magmatic differentiation of this 
gabbroitic magma has been locally increased through the fusion with 
it of granite and grano-diorite.”’ 
Prof. E. A. Wiilfing (of Kiel), ‘‘A Note on the Pigments of 
Minerals,” describes experiments on the subject of the pigments in 
‘coloured minerals, leading to the important conclusion that pigments 
exercise no’ appreciable influence on the refraction of the minerals in 
which they occur. 
Dr. C. Hlawatsch (of Vienna), ‘“‘On the Amphibole of Cevadaes 
(Portugal),’’ describes an amphibole in the so-called arfvedsonite-gneiss 
of Cevadaes near Campo Mayor. It is intermediate in character to 
riebeckite and arfyedsonite, and Hlawatsch proposes to call it Osannite 
after Prof. A. Osann of Freibureg-i.-B. 
Dr. KE. O. Hovey (of New York), ‘‘ The Geology of the Guaynopita 
District, Chihuahua: <A contribution to the knowledge of the 
structure of the Western Sierra Madre of Mexico.” * ‘he oldest rock 
described is a semi-crystalline, much metamorphosed Cretaceous lime- 
stone, completely overturned and flexed in Guaynopita mountain. 
This folding was followed by the eruption of andesitic breccias, ash 
and flows, which are probably somewhat unconformable to the lime- 
stone; granite was then intruded, resulting in the completion of the 
elevation and metamorphism of the limestone; dacite, rhyolites, and 
basalt. were afterwards extruded. 
Prof. O. Miigge (of Konigsberg), ‘‘The Rate of Decomposition of 
Quartz in the presence of Hydrofluoric Acid: A contribution to the 
Theory of Etched Figures.”’ 
Prof. L. Milch (of Breslau), ‘‘ On Differentiation in Granitic Magmas 
from Observations on the Granite of the Riesengebirge.”’ 
Prof. M. Koch (of Berlin), ‘“‘ Note on the Olivine-diabases of the 
Upper Harz.” 
Dr. R. A. Daly (of Ottawa), ‘The Differentiation of a Secondary 
Magma through Gravitative Adjustment.” * The paper describes the 
Moyie sill of hornblende-gabbro intrusive in quartzite in the Purcell 
Mountains, on the boundary between British Columbia and the United 
States. At the upper junction of the sill with the quartzite an 
abnormal biotite - granite is developed, which Daly attributes to 
digestion of quartzite in the hornblende-gabbro, at both the upper and 
lower contacts of the sill. He supposes the material digested at the 
lower contact to have mostly risen by gravitation through the whole 
thickness (840 metres) of the sill and accumulated at the upper contact. 
Dr. EK. Becker (of Heidelberg), ‘‘ The Wartenberg near Geisingen 
in Baden.’’ The columnar nepheline-melilite-basalt and associated 
eruptive breccia of the Wartenberg are allied to the other Swabian 
embryonic volcanoes (of Branco), and are to be regarded as filling 
a volcanic neck. The neighbouring Fiirstenberg is believed to conceal 
a similar volcanic nucleus. 
