Moss—On a Graphitic Schist from Co. Donegal. 207 
From the external characters of the rock it would not be sup- 
posed that it contains little more than 3 per cent. of carbon. It 
has the lustre of graphite, though of a grayish tint, and possesses 
the foliated structure so frequent in that mineral. It soils the 
fingers like graphite, but marks paper badly. Comparing the com- 
position of the ash with that of the ash of graphite, the quantity 
of alkali present in this rock is large. In the case of fifteen 
analyses of graphite, quoted by Dana and Brush in their “System 
of Mineralogy,” the largest quantity of alkali in the ash is 2°2 
per cent., whereas in this graphitic rock there is 7:27 per cent. of 
the oxides of potassium and sodium. 
SCIEN. PROC. R.D.S., VOL. VIII., PART III. 
