1072 The American Naturalist. [November, 
of carbon-dioxide, augite-porphyrite, granite, and granitic and syenitic 
porphyries. Each of these rocks is described, and analyses of several 
of them and their constituents are given. The most interesting point 
brought out by the analyses has reference to the relation between the 
diallage of a gabbro and the secondary hornblende derived from it. 
SiO, ALO, FeO, FeO CaO MgO Na,O K,O H,O 
Diall. 59.630042 5.09 13.54 0.19 18.77 “57 29 
Horb. 52.73 4.70 5.26 10.21 12.58 12.59 .23 .06 1.54 
An increase in CaO and decrease in MgO in passing from diallage to 
hornblende is in opposition to the view held in regard to the nature of 
the change. The author is compelled to look upon it as paramorphic. 
Cathrein * has re-examined the rock from Ehrwald in the Tyrol, 
called by Pichler augite-porphyry, and thought by Rosenbusch to 
belong possibly with the teschnites, and has found it to consist of 
phenocrysts of augite, both monoclinic and orthorhombic, in a 
ground-mass composed of crystals of biotite, pyroxene, hornblende, 
apatite, and magnetite, in a base containing some radially fibrous 
mineral in an isotropic substance. The rhombic-pyroxene has been 
changed to bastite, which is intergrown with biotite and augite, and is 
surrounded by small crystals of augite of the second generation, of 
hornblende, and of biotite. The augite of the ground-mass is groupe 
in aggregates resembling chondrites, and is pleochroic in violet and 
yellowish-red tints. The author classes the rock with the augitites, and 
calls it bastite-augitite or Ehrwaldite——Spherulites composed of 
radiating bundles of an alkaline feldspar and spherical masses of tridy- 
mite occur in the obsidian of the Lipari Islands, according to Mr. 
Iddings.? They are similar to the spherulites and lithophyse of the 
rock from Obsidian Cliff, and contain, like the latter, little honey- 
yellow crystals of fayalite——In an appendix to an article by Mr. 
Barlow® on the contact of the Huronian and Laurentian rocks north 
of Lake Huron, Dr. Lawson briefly describes a few sections of quartz- 
ites on the contact with gneisses, in the former of which he believes 
are evidences of contact alteration, in which event the gneisses must 
be regarded as eruptive. Mr. Fairbanks? has examined eighty sec- 
tions of basic dykes from the north shore of Lake Huron, and has 
found them to be diabases, diorites, and alteration products of these- 
5 Verh. d. k. k. geol. Reichsanst, I., 1890, p. 1. 
1 Iddings and Penfield, Amer. Jour. Sci., July, 1890, p. 75- 
8 Am. Geologist, July, 1890, p. 19. 
9 Tb., Sept., 1890, p. 162. 
