696 The American Naturalist. [August, 
The fact that at the nearest exposures the calciferous lies directly 
upon crystalline rock is the author’s reason for referring the last two 
doubtful rocks to the Algonkian or Archean. (Proceeds. Rochester 
Acad. Sci., Vol. i, p. 182.) 
MINERALOGY AND PETROGRAPHY!:' 
The Eruptives of Cabo-de-Gata.—The eruptive rocks of the 
Cabo-de-Gata region in southeastern Spain are pumiceous, glassy and 
granular liparites, andesites, dacites and an occasional basanite. The 
liparites are rare as fragments in a liparitic tufa and as small dykes 
cutting the fragmental rocks. The dacites cover a large stretch of 
country. They are the most abundant types in the region, and are 
developed in great variety. Two principal groups are distinguished. 
The first is characterized by the abundance of its phenocrysts, among 
which are large hornblendes, and by the possession of augite and hypers- 
thene. Augite occurs in their groundmass, quartz is scarce, and their 
feldspar is almost exclusively plagioclase. In the second group phen- 
ocrysts are less common. Biotite is the predominant colored constit- 
uent. Quartz and sanidine are both plentiful and the rock thus 
verges toward the liparites. All the components of these dacites have 
been very minutely described by Osann? But few of them present 
special peculiarities. The most interesting features connected with 
them are the alteration of hornblende into pyroxene and the intergrowth 
of augite and bronzite, with the pinacoids and prisms of the two minerals 
parallel. The andesites, which are best developed in the southern and 
southeastern parts of the region, are hornblendic and biotitic varieties. 
mica andesite from the Rambla del Esparto contains an enormous 
number of granular inclusions composed of cordierite (?) biotite, 
spinel, sillimanite, corundum, andalusite, plagioclase, rutile, zircon, 
garnet, quartz and apatite. They are regarded as having resulted 
from the metamorphism of blocks brought from below, and the crys- 
tallization of andesite components upon them. The spinel occurs in 
dark-green and grayish-red crystals, the former sometimes surrounding 
the latter. A dacite from Mazarron contains phenocrysts of cordier- 
ite,’ whose prismatic crystals often reach a length of 1 cm. The forms 
_ 1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me. 
*Zeits. d. Deutsch. Geol. Ges. 1891, xliii, p. 688. 
"Cf. AMERICAN NATURALIST, 1890, p. 69. 
Sry See eee ae T 
BOON NAS eI EE NS 
