Tirr: gkanulitk of kkkni-: tyi'k locality 



257 



Ci'oss-sedion. — Figure 7 represents a section paced olf in a brook near 

 the larofest mine. The strata dip westward toward tlie main range of 

 hills and away from Keene valley. The black ]u)rnl)len(lic schists are 

 not lacking at neighl)oring exposures, i)ut they do not show in the sec- 

 tion which is made uj) of two bands of limestone separated and bounded 

 by a dense garnetiferous rock. 



Petrography and Mincralogi/ — The Granulite. — In thin sections this 

 garnetiferous rock is seen to contain in addition to garnets untwinned 

 feldsjKir, a little plagioclase, green augite and a little apatite ; no other 

 minerals are present. It is thus a granulite and closely analogous to 

 the i)yroxene-granulites of Saxony. The association of such rocks with 

 limestones and iron ores in Sweden in similar relations to the al)ove 

 occurrence has been described''^ by Tiirnebohm. l)cs[)ite the general 

 lack of twinning, it would seem as if this untwinned feldspar must be, in 

 part at least, plagioclase. Some twins do occur, but this is not true of 



>&»ANUHT£ BREAK ANGRTHOSJTE w 



200VDK »» 



Figure 7.— Cross-section near Weston Mine, Keene. 



the great majority of the crystals. Of these untwinned crystals the ex- 

 tinction is often parallel b^ the cleavage, but it may reach 2o degrees. 

 The microperthitic growths are very widespread. One crystal with two 

 good cleavages was detected which gave an axial l)ar parallel to one of 

 them and was shown l)y the quartz wedge to be negative. It must be 

 orthoclaae. Microchemical tests on another specimen 3aelded lluosili- 

 cates of potash in considerable amount — of soda and of lime rather more. 

 The conclusion is unavoidable that both orthoclase and plagioclase are 

 present, the latter ranging as basic as labradorite. George Hawesf 

 showe<l years ago that twinning might fail in plagioclase, and especially 

 in the labradorite of an(M-thosites. As this socalled granulite is regarded 

 as a contact facies of anorthosite, this coincidence is notable. It is (juite 

 possible that natron-orthoclases are also present, with microperthitic 

 growths analogous to those which have been found by \V. ('. Hnigger in 



Norway. 



•Neaes Jahrl.uch. 1874. p. 138. 



tG. W. Hawes: On the Determination of FelilHpnr in thin SoctionH of Roijks. Proc. U. S. National 

 MaHoum, 18^1, p. VM. 



XXXVI- Bill., (iv.ot.. Sor. Am.. Vol. R. 18!»4. 



