135 



Ophite. This name has been applied to certain basic igneous rocks occur- 

 ring in the Pyrennees. The true character and relationships of the different 

 varieties have not been fully worked out. It must therefore be regarded as a 

 local term applied to rocks of somewhat variable character. Plagioclase, 

 augite, diallage, hornblende, and brown mica enter into the composition of 

 these rocks. Where the rocks are largely composed of plagioclase and augite 

 the latter mineral usually occurs in large irregular masses, which include and 

 are penetrated by the felspar prisms. This mode of arrangement (see 

 Plate X., Fig. 1.) has been designated by M. LEVY as the ophitic, and the 

 term is used in this sense in the present work. 



Proterobase. This term is due to GUMBEL. (I) The rock consists of green 

 or brown, not strongly fibrous hornblende, reddish brown augite, plagioclase, 

 a chloritic mineral, magnetite or ilmenite, and in most cases a magnesian mica. 

 Some of the proterobases of GUMBEL have been shown by LOSSEN (2) and 

 LIEBE (3) to be normal plagioclase-augite rocks (diabase,) altered by contact 

 and pressure-metamorphism. Thus, a rock from Winzenberg in the Hartz, 

 described by ROSENBUSCH as a typical proterobase has been shown by LOSSEN 

 to be a normal diabase altered by contact with granite. Precisely similar 

 rocks have been described by Mr. ALLPORT (4) in his classic paper " On the 

 Metamorphic Rocks surrounding the Land's End Mass of Granite." 



Epidiorite (GUMBEL). The rock is defined as a mixture of fibrous, pale 

 green needle-shaped hornblende, often much altered, plagioclase, a chloritic 

 mineral and ilmenite or magnetite. Augite is absent, or present only in very 

 small quantity. According to LIEBE (loc. cit.) the epidiorites are diabases 

 that have been affected by regional metamorphism. They occur in the zone 

 of maximum metamorphic action. 



Leucophyr (GUMBEL). This rock is distinguished from normal diabase by 

 its pale colour, due to the predominance of the felspathic constituent. It is 

 defined by GUMBEL as consisting of a saussuritic plagioclase, pale green augite 

 (without hornblende, and rarely with reddish brown augite) in very small 

 quantity, a chloritic mineral and ilmenite. ROSENBUSCH refers certain rocks 

 intercalated with the Steiger Schiefer of the Vosges to GUMBEL'S leucophyre. (5) 



The epidiorites, proterobases and leucophyres of GUMBEL are all associated 

 with lower paleozoic sediments, and appear to have been involved with the 



(1) Die palseolithischen Eruptiv-gesteine des Fichtelgebirges, Munich, 1874, p. 9. 



(2) Studien an metamorphischen Eruptiv- und Sediment-gesteinen. Jahr. d. k. Preuss. 

 Geol. Landesanstalt, 1883, p. 619. liber das Auftreten metamorphische Gesteine in den alten 

 palaozoischen Grebigskernen von der Ardennen bis zum Altvatergebirge und iiber der Zusam- 

 merhang dieses Auftretens mit der Faltenverbiegung (Torsion) Sits. d. Gee. natur. Freunde, 

 Berlin, 1885, p. 32. 



(3) Ubersicht iiber der Schichten-aufbau Ostthuringens. Abhand. z. geo. Specialkarte v. 

 Treussen u. d. Thiiring. Staaten. Bd. V., Hft. 4. 



(4) Q.J.G.S. 1876, XXXII., p. 407. 



(5) A specimen from the Vosges labelled Leucophyre, Breitenbach, in the author's posses- 

 sion, contains uralitic and actinolitic hornblende of a pale green colour, but is entirely destitute of 

 augite. The felspar in many places is perfectly colourless, and occurs in irregular granular 

 aggregates. The rock, in short, has not the microstructure of a normal igneous product, but 

 gives evidence of having been subjected to contact on pressure metamorphism. It seems prob- 

 able therefore that in this case we are dealing with a plagioclase-augite rock which has been 

 involved in the earth movements that have affected the sediments with which it is associated. 



