330 Scientific Geology. 



served fragments of mica slate cemented by the hydrate of iron, so as 

 to form a conglomerate. (No. 716.) It is, however, of very limited 

 extent ; occupying only occasional fissures in the rock, and is probably 

 the result of slow disintegration, and the subsequent infiltration of 

 iron from the decomposition of pyrites. 



In the vicinity of the sienite in Whatley, I found a bowlder, obvious- 

 ly compose^ of fragments of mica slate, which were once partially 

 fused. They are cemented together chiefly by feldspar. The nu- 

 merous nodules of the mica slate imbedded in the sienite at that place 

 will render this explanation rational, as I shall attempt to show in de- 

 scribing sienite. (No. 724.) 



12. Indurated Mica Slate. In the same region in Whatley, I 

 found a bowlder between quartz and chert, of a dark gray colour, ex- 

 hibiting traces of an original slaty structure. (No. 725.) As Dr. 

 Macculloch says of a similar variety found in Scotland, " it is not enu- 

 merated with the siliceous schists, because it has not been the prac- 

 tice so to do; but it bears a strong analogy to the primary varieties of 

 these."* 



13. Augite Rock. It may not be expected to see this rock placed 

 in this connection : since the rock of this name described by Dr. 

 Macculloch in Europe, is an unstratified overlying rock, associated 

 with basalt and greenstone. But the one here introduced, is of en- 

 tirely a different character. It is ordinarily composed of granular 

 and semicrystallized augite, of a greenish or yellowish color, mixed 

 with quartz in small quantity ; and is interstratified with mica slate 

 and hornblende slate. And since it occurs in too small a quantity to 

 be described as a distinct rock, I thought the proper course would be 

 to notice it in this connection. (Nos. 726, 727.) I have found it only 

 in Williamsburgh, two miles west of the meeting house, at the local- 

 ity of smoky quartz and plumose mica ; where its characters corres- 

 pond with those mentioned above. But Dr. Emmons informs me 

 that it exists in Chester in the situation exhibited below : that is, there 



"2 *^i ^ *2 



* Classification of Rocks, p. 280. 



