1887] _ | Mineralogy and Petrography. 471 
MINERALOGY AND PETROGRAPHY. 
Petrographical News.—A fe l 
have recently been described By Séhmidt? pie the dete side of 
the Central Alps in Switzerland. Near Iberg, in Canton Schwyz, 
a diabase porphyrite occurs cutting Eocene deposits. This por- 
phyrite presents all the characteristics of pre-Tertiary porphyrites. 
It offers another proof of the fact that texture in rocks depends 
more upon the conditions under which the rock magma solidified 
than upon the age during which it was erupted. The porphyritic 
crystals are oligoclase. Many of them consist merely of an outer 
shell of plagioclase substance, including material identical with 
that of the ground-mass. elaphyres from near Glarus contain 
olivine crystals, which have undergone the unusual alteration 
into bastite. essrs. Barrois and Offret3 have found that the 
rocks of the Sierra Nevada Mountains in Southern Spain are 
similar in many respects to those of the Ronda* Mountains. 
They consist principally of a series of highly-altered schists and 
limestones. The mica schists of this series contain in addition 
to their essential constituents the accessory minerals rutile, 
tourmaline, garnet, muscovite, kyanite, sillimanite, andalusite, 
and occasionally feldspar. Garnet and staurolite are among the 
oldest constituents, Their shattered condition shows that the 
rock in which they occur has been subjected to great pressure. 
The Cambrian schists of this region are divided into sericite 
rounding rock-masses. mong the Cambrian amphibolites is 
mentioned a variety ena glaucophane, with a Spaa 
blue tint instead, of a violet- blue color parallel to b. The c 
position of this. Siracoptant I is 
SiO, - AlO, FeO MgO CaO NaO  lossatred heat 
47-42 8.42 9.68 15.28 12.95 2.97 4.16 
——A dyke of diabase cutting the old red sandstone near Dum- 
barton, Scotland, is described by Lacroix as presenting a fine 
example of the existence in the same rock-mass of three distinct 
pes of structure,—the devitrified glassy, the porphyritic, and 
the ophitic, The analyses of several rocks from the neigh- 
borhood of Christiania, Norway, have recently been published.® 
The rocks analyzed are, with one exception, from the area occu- 
z Edited by Dr. W. S. BAYLEY, Madison, Wisconsin. 
2 Neues Jahrb. f. Min., etc , 1887, i. 8. 
6 Jannasch, Ber. d. deuts. chen. ` Gesell., 1887, i. p. 167. 
