Dr. F. H, Hatch—A Peridotite from Kilimayaro. 259 
The olivine is perfectly fresh and consequently colourless. High 
magnification discloses, both in this mineral and in the hornblende, 
the presence of parallel rows of opaque rod-like enclosures. The 
freshness of the minerals that contain them seems to preclude the 
idea of these bodies being of secondary origin. 
The iron-ore occurs in irregular opaque grains which are easily 
attracted, and removed from the powdered rock, by a small 
bar-magnet. These grains are often edged by irregular plates of 
a translucent green mineral, which also occurs in isolated grains, 
or included in the hypersthene. In the latter case it sometimes 
assumes an octahedral form. It is isotropic and belongs probably to 
the spinell-group (pleonast or hercynite). 
With regard to the name applied to this rock, its right to a place 
among the peridotites is at once established by its high density 
(sp. g.=3'3), the complete absence of a felspathic constituent, and 
the presence of a considerable proportion of olivine; although the 
latter is not the dominant constituent. Were the classification 
advocated in the new edition of Rosenbusch’s ‘‘ Physiographie der 
massigen Gesteine”* to be followed, the rock would have to be 
referred to the hornblende-picrites. Since, however, it bears no 
resemblance in structure and composition either to the rocks to 
which Tschermak originally gave the name picrite, or to those, 
for which 15 years later Prof. Bonney proposed the name horn- 
blende-picrite, I do not feel justified in adopting these terms. 
Indeed no small confusion seems to have been caused, here as in 
other cases of rock-nomenclature, by the modification in the meaning 
of a term, the extension of which has been clearly limited by its 
originator. 
The name picrite was given by Tschermak,’ in 1866, to crystalline 
rocks which are intrusive in the limestones and sandstones of 
the Cretaceous and Eocene formations of the highlands between 
Neutitschein, Teschen, and Bielitz, in Moravia and Silesia. These 
rocks “are described as consisting “to the extent of one half of 
crystals and grains of olivine; further of a lime-felspar, together 
with diallage, which can be replaced by hornblende, augite or biotite. 
The texture is porphyritic, with regard to the olivine, or finely 
granular.” . .. . “ Picrite bears the same relation to olivine-gabbro 
as basalt or melaphyre to gabbro.”* Like basalt it often possesses 
‘an interstitial substance which consists partly of microlites, partly 
of a structureless isotropic glass.” * 
Later on we find Giimbel ° applying the term palcopicrite to altered 
rocks which consisted originally of olivine, pyroxene, and a small 
this author, to crop out at the very foot of Kilima-njaro on the E. and S. sides. O. 
Miigge (Neues Jahrb. B.B. iv. 1886, p. 576) has described gneissose mica-schists 
and amphibolites from the southern portion of Massai-Land, as constituting members 
of a ‘‘ gneiss or granite-gabbro formation.’’ 
1 1887, p. 260. 
2 Sitzungsber. K, K. Akad. der Wissensch. Wien, 1866, Bd. liii. p. 260. 
 Sitzungsber. K. K. Akad. der Wissensch. Wien, 1867, Bd. lvi. p. 274. 
* Die Porphyrgesteine Oesterreichs, etc. Wien, 1869, p. 245. 
° Geogn. Beschreib. des Fichtelgebirges, Gotha, 1879, p. 150. 
