260 Dr. F. H. Hatch—A Peridotite from Kilimayaro. 
quantity of plagioclase and brown mica. The new word was scarcely 
wanted ; but still an intelligible use can be made of it, if it be noted 
that the palzopicrites bear the same relation to the diabases that 
the picrites do to the basalts. In short the paleopicrites are olivine- 
diabases in which the felspar is quite subordinate. In this country 
we have as examples of typical paleopicrites, the Blackburn and 
Inchcolm rocks, described by Dr. A. Geikie.! 
In 1881 Prof. Bonney? proposed the subdivision of the picrites 
into hornblende-picrite and augite-picrite, according as the dominant 
bisilicate is hornblende or augite. Adopting this subdivision, 
Rosenbusch, in his new edition, has defined the hornblende-picrites 
as peridotites which consist essentially of olivine and hornblende, 
and the picrites as peridotites which consist essentially of olivine 
and augite, the term peridotite being restricted to “plutonic rocks 
(Tiefengesteine) with hypidiomorphic-granular structure and charac- 
terized by the absence of felspar and the presence of abundant 
olivine.” This, it will be seen, is a considerable change in the 
meaning originally attached by T'schermak to the term picrite ; and 
the latter, as defined by Rosenbusch, admits of considerable variation 
in structure and affinities. On the other hand, Tschermak’s picrites 
(e.g. that from Giimbelberg near Neutitschein) have been relegated 
to a new group, viz. that of the “ picrite-porphyrites.” * 
The conclusion to be drawn from these digressive considerations 
is that the picrites (or paleopicrites) are olivine-augite rocks which 
possess affinities with, and pass, by an increase in the amount of 
felspar, into dolerites (or diabases) and basalts; while the horn- 
blende-picrites, on the other hand, appear to be rocks which possess 
affinities with, and pass into, diorites. 
The peridotite from Kilima-njaro, described above, contains no trace 
of felspar, has a specific gravity of 3:3, is holocrystalline and granular, 
and exhibits indications of foliation—characters which are incom- 
patible with those of the picrite group. It bears, however, some 
resemblance to the hornblende-peridotites of Peekskill, Hudson 
River, N.J., described by G. H. Williams ;‘ and I have therefore 
followed his system of nomenclature. If a distinctive name were 
really requisite, the name Cortlandtite, suggested by Williams for 
these rocks because of their relation to the Cortlandt series of Dana, 
might be adopted. 
Mr. Teall has shown me peridotites from Scourie in Sutherland- 
shire, which bear a still more striking likeness to the Kilima-njaro 
rock.° 
1 Trans. Roy. Soc. Edin. vol. xxix. (1880), p. 504. 
2 Q. J. G. 8S. vol. xxxvii. (1881), p. 137. 
3 Physiog. der Massig. Gest. 1887, p. 518. 
* Amer. Journ. of Sci. vol. xxxi. 1886, p..26. 
y ae Scourie rocks are placed by Rosenbusch among the hornblende-picrites, 
l.c. p. 267. 
