186 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull.165; 
nounced in the black areas. Between crossed nicols the black is iso- 
tropic, and the yellow spots are but faintly birefringent. A great 
quantity of iron dust seems to be present, and probably some glass also. 
The slates included in the rock are hard, gray fragments composed 
of minute quartz and feldspar grains, together with secondary chlorite 
and calcite. 
The specimen from Castle Hill is very badly decomposed, but the 
abundance of apatite, the presence of the A T iolet augite, and the general 
structure of the rock all indicate similarity to the typical teschenite of 
Mapleton. 
