Professor Emerson on IlaWs Geological Collections. 563 



black mica granite like No. 35. It has splintery fracture, and shows glistening 

 points of quartz upon fresh surfaces. 

 51). Petrosilex. 



A fresh leek-green felsite or petrosilex weathering white, agreeing closely 

 with the green petrosilex from Pelham, Mass., which has passed under the name 

 of "Shay's flint:" and this rock proves, like that from Pelham, to be a very 

 fine-grained silicious variety of horublendic gneiss. This conclusion is based on 

 a study of thin sections of both varieties. 

 GO. Banded hornblendic gneiss. 



Greenish -black granular hornblende, granular quartz, and some feldspar, 

 mostly triclinic. The banded structure is caused by the interijosition of more 

 compact layers of quartz and feldspar; a little biotite present in brown decom- 

 posed scales. 



61. Banded hornblendic gneiss. 



A large mass similar to 60, the dark layers finer grained, and the quartz- 

 feldspar layers thick and irregular. 



62. Hornblendic gneiss. 



A thin laminated rock, containing abundantly white to greenish muscovite, 

 dark brown hornblende, quartz, and feldspar ; the latter in one instance triclinic. 

 The very bright pearly luster of the mica gives the rock a peculiar sheen upon 

 the cleavage face which disappears entirely in other directions. 



Labeled, " Azoic Eocks, Probisher Bay." 



63. Hornblendic gneiss. 



Granitoid, with white and red feldspar, black granular hornblende, and 

 green mica. 



Locality, French Head, Field Bay. 



64. Foliated hornblendic gneiss. 



Thin folia of black to greenish-black hornblende, separate broader bands of 

 a mixture of milk-white orthoclase and quartz, forming a rock of very attractive 

 appearance. 



65. Syenite. 



Granitoid and of medium grain. The rounded spots of white orthoclase 

 stand out on a background of blackish-green hornblende. 

 Labeled, " Azoic Eocks, Frobisher Bay." 



66. Hornblende schist. 



Several pieces of schist, consisting of black granular hornblende and quartz, 

 in one case containing a little triclinic feldspar and chalcopyrite. 



