Rocks of Noyang. 61 



mined a slice prepared from a dense black fragment included 

 in the quartz-mica-diorite at the immediate contact. I found 

 it to be a metamorphosed sandstone, exactly similar to some 

 occurring at Swift's Creek. It was composed of (1) quartz 

 grains, (2) muscovite, (3) biotite. I have placed these in the 

 order in which they are relatively as to amount. The only 

 peculiarity in this sample is that the biotite mica is, in 

 places, almost wholly aggregated together, leaving other 

 spots free from it. Besides these three principal constituents, 

 there were numerous minute flakes of brown mica scattered 

 throughout the whole slice, and of such minute size as to be 

 little more than mere microliths. 



In order to compare, if possible, the most altered with the 

 least altered rocks, I selected an example of a finely crystal- 

 line hornfels, which seemed to nearly represent the less 

 altered rock which I have examined and analysed (No. 8), 

 Of this I prepared slices, and carried out a quantitative 

 analysis. 



Under the microscope I found it to consist of the follow- 

 ing minerals : — (1.) Angular quartz grains, with their longer 

 diameters approximately parallel. (2.) Biotite mica in brown 

 ragged flakes, forming foliations, but also scattered through 

 all the rock. This mica is dichroic in shades of brown. 

 (3.) A colourless mica, in long rectangular flakes, having the 

 characters of muscovite. (4.) A chlorite mineral in small 

 aggregations, filling-in spaces in the mass ; it is pale green, 

 and not sensibly dichroic. (5.) Brown iron ore ; and (6.) a 

 few small prisms of tourmaline. 



