452 DESCRIPTIONS OF ROCKS. 



The ''antique green porphyry," or Porfido xerde antico, figured on 

 page 415, in fig. 2, is a porphyritic rock of the composition of doleryte, 



the feldspar being labradorite. and the other chief constituent, augite, 

 with also some chlorite, or viridite, whicb last is the source of the 

 greenish color. It is from the South Morea, between Lebetsova and 

 Marathonisi. Delesse obtained, from the compact base, Silica 53 '55, 

 alumina 19 '34, iron protoxide 7 35, manganese protoxide 0'85, lime 

 8'02, soda and potash T'93, water 2"6T. In view of its firmness, and 

 its contrast in this respect with most chloritic doleryte, it may be 

 queried whether the rock is not a mttamorphic doleryte inietadolerytei. 

 It closely resembles the porphyritic labradioryte from the vicinity of 

 New Haven, Conn, <wh.ich.is cbloritic and metamorpbic •, though differ- 

 ing from it in containing pyroxene instead of hornblende. A similai 

 porphyry is reported from Elbingerode in the Hartz, Belfahy in the 

 Vosges, and Barnetjern near Cbristiania in Norway. 



5. Eucryte. — A doleryte-like rock consisting chiefly of an- 

 orthite and augite. Occurs compact, and as a lava/ From 

 Elfdalen, Xorway. 



6. Amphigenyte. (Leucitophyre.) — Contains augite, like 

 doleryte. but leucite (called sometimes ampliigene) replaces 

 the feldspar. Dark gray, fine-grained, and more or less cel- 

 lular to scoriaceous. G. — 2 # 7— 2*9. The leucite is dissemi- 

 nated in grains or in 24-faced crystals. Constitutes the 

 lavas of Vesuvius and some other regions. Accessory min- 

 erals, nephelite, biotite, chrysolite, sodalite, sanadin, labra- 

 dorite and nosean. 



Hauynophyre is an amphigenyte from Vulture, near Melfi, in which 

 haiiynite replaces much of the leucite. 



7. Nephelinyte. (Xepheline-doleryte.) — Contains augite, 

 like doleryte, but nephelite replaces the feldspar, or the larger 

 part of it. Crystalline-granular ; ash-gray to dark gray. 

 The nephelite is partly in distinct crystals. 



8. Tachylyte. Hyalbmelan. — Blackish glass, or pitchstone, 

 made in connection with augitic igneous rocks or lavas ; 

 the former affords on analysis 49 pef cent, of silica, and the 

 latter 55. 



This Dohrytt -pitchstone may be porphyritic, or contain small grains 

 of augite, or of chrysolite. 



7. PYROXENE, GARNET, EPIDOTE. ahd CHRYSOLITE ROCKS, 

 CONTAINING LITTLE or XO FELDSPAR. 



1. Pyroxenyte. — Coarse or fine granular pyroxene rock. 

 Sometimes chrysolitic. a varietv which occurs with chryso- 

 litic hornblendyre at the localities mentioned on p. 446. * 



2. Ganietyte, or Garnet Rock. — A yellowish-white to green- 



