334 RECORD OF SCIENCE FOR 1887 AND 1888. 



tbe edges and preserved the olivine whicli bad formed prior to its injec- 

 tion. The inner portion remaining longer liquid and becoming more 

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



Barrois* has sbowu from a, stndy of tbe contact i)benomena of the 

 granites of Morbi ban that two forms of metamorphism occnr, both strnct- 

 ural, the one due to rai)id cooling and the second to mechanical agen- 

 cies. In tbe tirst there is a transition irom even granular to porpbyritic 

 oraplitic forms. In tbe second a schistose form is produced only at tbe 

 periphery of the mass and due wholly to powerful mecbanical agencies. 



Greimt has described in great detail an occurrence of contact phe- 

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

 and the adjacent schists. Here tbe diabases remain practically un- 

 changed, but that they are of finer texture at the contact, wbile the 

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

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

 tropic grouudmass in which are quartz, audalusite, spinel, and a chloritic 

 mineral. The change has taken place witb a very decided increase in 

 tbe amount of soda and iron, supplied apparently by the diabase. 



Riidemannf 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 and in itself has suffered no other than 

 structural modifications and a slight increase in the proportional amount 

 of biotite. At contact bofli phyllites and slates are converted into a 

 bard, compact, blue-black hornfels consisting of a crystalline-granular ag- 

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

 and audalusite. This zoue, some 120 paces in widtb, is succeeded by a 

 second some 380 paces in width of andalusite mica schist and this by a 

 spotted mica schist {Knoten-Scbiefer) some 500 paces wide. Lastly the 

 least altered rock, tbe cbiastolite schist zone, some 400 paces wide, de- 

 rived from the clay slates, or a biotite rock (Garben-Schlefer) from the 

 pbyllite. Itis noticeable thatinall these cases the chemical composition 

 of the altered rocks is tbe same as that of the unaltered beds from whicb 

 they are derived, no new matenal 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 tbe slates and phyllites. The line of contact between the 

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

 and distinct. Tbe entire widtb of the metamorphosed zone was in the 

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

 some 1,400. 



DYNAMIC METAMORPHISM. 



Our knowledge on tbe subject of dynamic metamorpbism lias likewise 

 been very materially increased. The question of the origin of the foli- 



" Ann. de la Soc. G^ol. du Nord, November, 1887, 

 tNenes Jahrb., 1888 1. B., 1. Heft, 

 t Ne^ea Jabrb., v, Bell. -Band, p. 6^, 



