THE GOSHEN SCHISTS OR FLAGS. 183 



the micro.scf)pe as it is in the field, uud may be called a bastard giuiiss 

 or a feldspathic sandstone gi'own biotitic Vjy metamorphisin. 



Granitoid hiotite-gnciss from near the great pegmatite dike at the sonth 

 end of South street, Chesterfeld ; from a thick stratum, conformably intei'- 

 bedded in the spangled mica- schist near its baae. It bears a close resem- 

 blance to the Becket gneiss. 



A light-gray, fine-grained, biotite granitoid gneiss, the scanty Ijiotite 

 scales rounded or hexagonal, separate, and at times deep-red under the lens. 

 The quartz and feldspar are colorless; the latter is glassy, often .showing 

 strijB. Under the microscope it is remarkably and unexpectedly fresh, only 

 here and there is a muscovite gi'owth accenting the twinning of a plagio- 

 clase It is, furthennore, very unlike the Becket gneiss, with which it 

 agrees macroscopically. 



Th(; quiirtz shows ]iriinary grains marked out by iron rust and second- 

 ary quartz in lobed, interlocked masses. The abundant traces of water 

 pores generally contain globules, but these are of small size and oidy rarely 

 show motion They are unaffected by heat The quartz contains in con- 

 siderable abundance the ratile (?) trichites. 



The orthoclase is generally in carl.sbad twins, and shows the most 

 remarkable wavy extinction. Microcline is well represented. The plagio- 

 clase shows an extinction of 10° and 4° on each side the twinning plane. 

 The biotite is wholly unlike that in the Becket gneiss, and resemljles 

 closely the biotite of the mica-schists, with which it is associated. It is 

 bright brownish-red, with strong dichroism and no tendency to change 

 into green foi-ms It shows jjarallel intergrowth Avith muscovite, and is 

 surrounded at times with a band of muscovite scales. It incloses apatite. 



Muscovite appears only microscopically, and besides its association 

 with biotite shows at times a beautiful microplumose stracture. 



Apatite occurs in great abundance. Opaque iron ore, titanite, rutile, 

 and zircon are wholly wanting. 



THE COXWAY SCHISTS, OR THE CORRUGATED >nCA-SCHISTS. 



GENERAL DESCRIPTION. 



This widely extended foi'mation (the upper portion of the calciferous 

 mica-schist) is a dark-gi'ay to black, quite highly graphitic muscovite-schist, 

 so shaqjly comigated that the foliation surfaces are often wholly lost in a 



