146 GEOGNOSY. —— [Boox I. 

sense in which it is used requires to be explained. Senft’ described 
melaphyre as an indistinctly mixed rock, dirty greenish-brown, or 
reddish-grey, or greenish black-brown to black; bard and tough 
when fresh (but also often with a pitchstone-like greasy lustre or 
like basalt), and showing crystals of reddish-grey labradorite, with 
magnetic titaniferous iron, and usually with carbonates of lime and 
iron, and ferruginous chlorite (delessite), and a crystalline granular 
or compact, earthy, porphyritic or amygdaloidal texture. Naumann 
defines. melaphyre as a greenish, brownish or reddish-black micro- 
crystalline or crypto-crystalline, seldom slightly granular rock, with 
conspicuous dispersed crystals of labradorite, and less frequent and 
distinct crystals of pyroxene, not uncommonly rubellan or mica, but 
no quartz.” ~Zirkel in his first work. called it a generally crypto- 
crystalline, sometimes porphyritic, very often amygdaloidal mixture 
consisting essentially of oligoclase and angite with magnetic iron.? 
In his more recent synopsis of the microscopic characters of rocks 
he admits the great diversity that has prevailed in the use of the 
term melaphyre, and the wide range of structure of the rocks that 
have been included under it. He regards the melaphyres as early 
precursors of the felspar-basalts, with but a rare development of a 
purely crystalline structure, and on the contrary a prominent non- 
individualized substance which may either be abundantly developed 
as a base or appear only sparingly between the crystals, and may be 
sometimes purely glassy, sometimes half-glassy, and sometimes 
completely devitrified.* 
Rosenbusch, after a, review of all the previous literature of the 
subject, proposes that the term melaphyre should. be restricted to an 
older massive rock consisting essentially of plagioclase, augite, olivine, 
with free iron oxides and a porphyry base of any structure, and in 
variable proportions, and belonging for the most part to the age of 
the Carboniferous or older Permian, less frequently of the Triassic 
formations.’ According to his arrangement, the old plagioclase-augite 
rocks are grouped in three sections; Ist, the granular section, including 
(a) Diabase, composed essentially of plagioclase and augite, and (0) 
coliyine-diabase, composed of plagioclase, augite and olivine; 2nd the 
porphyritic section (with a ground-mass), comprising (a) diabase- 
porphyrite—a diabase having a porphyry ground-mass, (6) melaphyre, 
containing olivine in addition to the plagioclase and augite ; 3rd, the 
vitreous section, in, which the subordinate glassy varieties of the 
diabase-porphyrites are embraced.° 
The attempt to base a classification of eruptive rocks upon 
chronological considerations has been fruitful of mistakes by leading 
to false assumption regarding the age of igneous rocks. The so-called 
mela hyres, like the diabases, do not differ in any essential feature 
of structure or composition from the basalts. fo entirely is this 
1 Classification der Felsarten, 1857, p, 263. 
2 Geol. i. p. 587. ® Petrographie, ii. p. 39. 
* Mik, Beschaf’. p. 411. 5 Mik, Physiog., p. 392, 6 Op. cit. p. 317. 
