THK TERRESTRIAL PERIDOTITES. — ECLVSITE. 117 



A. E. 214, from the same locality, is a similar, Ijut more highly altered rock, whicli 

 contains talcose material. 



The greenish talcose schists from ]\It. Ida are stated by Mr. iJiller to be associated 

 with and to pass into the olivine-ljearing rocks al>ove described from that locality. Ac- 

 cepting the accm-acy of his statement, it is proper to touch upon their microscopic charac- 

 ters so far as they bear upon this relation. 



A. E. 484 is a greenish talcose schist containing grains and crystals of magnetite. 

 Stained slightly with yellowish-brown ferruginous material from the decomposition of the 

 magnetite. The section is composed principally of talc holding magnetite and patches 

 of partly altered olivine and enstatite, traversed by a peculiar eozoon-like network of iron 

 ore, with the longest and best marked portions approximately parallel with an optic axis. 



A. E. 274 is a coarser greenish-gray talc schist, composed of talc and actinolite 

 (Diller's pyroxene) with iron ore and tlie remains of partially altered olivine. 



A. E. 270 is a beautiful green talc schist, containing crystals of actinolite and grains 

 and crystals of iron ore. Only a few olivine grains were seen. 



It seems to me from the study of these rocks, coupled with similar evidence obtained 

 from the examination of other rocks, like cumberlandite, that these schists and schistose 

 forms are the results of the alteration of peridotites : that is, the schists are derived from 

 the olivine rock, and not that from the schists. This view is, of course, opposed to that 

 of Mr. Diller and the majority of liLhologists and geologists. 



Variety. — Eulysite. 



Tunaherg, Norivat/. 



The rock from which this variety is named was first so called and described by Axel 

 Erdmaun, in 1849, as a granular mixture of diallage, garnet, and filtered olivine.* 



According to the later studies of H. von Mold, it contains fresh clear angular grains 

 of olivine cut by numerous fissures and holding much magnetite in powdery grains, while 

 the olivine is here and there altered into serpentine. A pale sea-green diallage occurs, 

 forming large grains in the rock. This diallage shows a fine fibrous parallel structure 

 (cleavage), which is often crumpled. This mineral often contains layers of very minute 

 lamince, which make with the cleavage planes angles varying from 20° to as much as 00° 

 or 70°. They are arranged in parallel lines. Pale almandine-red garnet in drop-like 

 rounded grains, and magnetite also, form constituents of the rock. Mcihl estimates the 

 percentages of the minerals as olivine (fayalite) 60 per cent, diallage 35 per cent, magne- 

 tite 3 per cent, and garnet 2 per cent.f 



The above description by Mold answers very well for the section in this collection 

 purchased from Richard Fuess. The general structure and relations of the crystals 

 indicate that the diallage and garnet, if not all of the minerals, are the results of a 

 recrystallization of the rock materials ; i. e. it appears to be a rock whose structure has 

 been produced by alteration and secondary crystallization, with but little if any of the 

 original structure and minerals remaining. 



KeUilsfjdll, S/rcdcn. 



According to Tornebohm, this rock is a fine granular one, greenish on the fresh 

 fracture, and weathering yellowish. Microscopically it is composed of irregular olivine 



* Nciies Jahr. Mia., ISiO, pp. 837, S3S. f Nyt Mag., 1877, xxiil. 119. 



