Io6 I'KNIII F:SKf)I.A. M.-N. Kl. 



Biotite and iipatilc were not separated from one other; the amount ol 

 the latter was estimated appi-oxiniately at i ^Vo, that of the biotite thus 

 being 5 O/O. 



The colourless main constituinls, (|uartz and plagioclase, sank on 

 dilution of the li(|iiid at the same time, ha\'ing a nearly identical specific 

 gravity. My efforts to estimate the relative amounts of these minerals by 

 the Rosiwal method failed in consequence of the unequal di.stribution, the 

 quartz occurring mainly as lenticular strings arranged parallel to the 

 foliation, while the plagioclase, in the form of smaller grains, chieflv ac- 

 companies the hornblende. But so much is certain, that the amount of quartz is 

 appreciably larger than that of the feldspar. The estimation of the quartz 

 at i8 and the feldspai" at 12.4 percent must be regarded as a' crude 

 approximation. 



The feldspar shows, in sections _[_ PM, extinction angles of about 10°. 

 A faint inverse zonal structure ma}' be seen occasionally. The average 

 composition of the plagioclase should not be far from Ab-^. 



For the dark brown biotite was assumed the composition of the 

 lepidomelane from granite. Cape Ann, Mass. (Quant. Classif. table XI\', e). 



Thus I arrived at the' following mode: 



Hornblende 39-4 



Quartz 18.0 



Garnet 16:4 



Plagioclase (Ab-.^) . . . 13,4 



Biotite 5.0 



Titanite 3.0 



Magnetite 3.0 



llmenite i.o 



Apatite 1.0 



100.2 



The specific gravity of the rock was directly determined at 3.146 

 (t -— 12^^). A calculation from the volumes of the minerals in the present 

 mode gives sp. g. = 3.16, the close agreement being a check that the mode 

 may be correct'. 



From these figures I calculated the following bulk composition of 

 this rock : 



' Errors in the mutual proportions of quartz and feldspar would, however, not intluence 

 the calculated sp. g. as both minerals are identical in their specific gravities. 



