334 RECOKD OF SCIENCE FOR 1887 AND 1888. 



the edges and preserved tlie olivine which hud formed prior to its iiijec- 

 tiou. The inner portion remaining longer li(|nid and becoming more 

 acid from the dissolved silica of the shales, redissolved the olivines. 



Barrois* has shown from a. study of the contact i>henomena of the 

 granites of Morbihan that two forms of metamorphism occur, both struct- 

 ural, the one due to rapid cooling and the second to mechanical agen- 

 cies. In the first there is a transition from even granular to porphyritic 

 oi'aplitic forms. In the second a schistose form is i)roducedouly atthe 

 periphery of the mass aud due wholly to i)owerful mechanical agencies. 



Greim t has described in great detail an occurrence of contact phe- 

 nomena between the olivine diabase near Weilburg, in Hesse-Nassau, 

 aud the adjacent schists. Here the diabases remain practically un- 

 changed, but that they are of tiuer texture at the contact, while the 

 schists, composed originally of quartz, white mica, and hematite with 

 lenticular beds of calcite, are converted into a compact rock vfith an iso- 

 tropic groundmass in which are quartz, audalusite, spinel, and a chloritio 

 mineral. The change has taken place with a very decided increase iu 

 the amount of soda and iron, supplied ai)parently by the diabase. 



Eiideinannf has described an interesting case of contact metamor- 

 phism in phyllites and clay slates at Reuth, near Gefrees, Bavaria. The 

 erupted rock is a biotite granite aud in itself has suffered no other than 

 structural modifications and a slight increase in the proportional amount 

 of biotite. At contact bot'h phyllites aud slates are converted into a 

 hard, compact, blue-black hornfelsconsistiugof a crystalline-granular ag- 

 gregate of quartz, deep reddish brown mica (biotite), a little muscovite, 

 and audalusite. This zone, some 120 paces in width, is succeeded by a 

 second some 380 paces m width of audalusite mica schist and this by a 

 spotted mica schist (Knoten-Schiefer) some 500 paces wide. Lastly the 

 least altered rock, the chiastolite schist zone, some 400 paces wide, de- 

 rived from the clay slates, or a biot'ite rock (Garben-Schiefer) from the 

 phyllite. Itis noticeable thatinall these cases the chemical composition 

 of the altered rocks is the same as that of the unaltered beds from which 

 they are derived, no new material having been supplied by the erupted 

 mass, though Riidemann would account for the formation of the hornfels 

 by the action of the heated waters accompanying the eruption upon the 

 materials of the slates and phyllites. The line of contact between the 

 granite and hornfels, it should be noted, is in all cases perfectly sharp 

 and distinct. The entire width of the metamorphosed zone was in the 

 case of the phyllites some 1,700 paces, and in that of the clay slates 

 someljiOO. 



PYNAMIC METAMORPHISM. 



Our knowledge on the subject of dyuamic metamorphism has likewise 

 been very nuiterially increased, The question of the origin of the foli- 



• Auu, ilela Soc, G6o\, d\\ Nord, November, lyti?. 

 t NeueH Jahrb,, 1S88 1. B.. 1. Heft. 

 t Neues Jahrb., v, Beil.-Band, p. 643. 



