348 



Scientific Geology. 



there, from the irregular action of the magnetic needle in the vicinity, 

 A full description of the spot was given by me in the 14th volume of 

 the American Journal of Science. In the 20th volume of the same 

 work, it has been suggested by Mr. Shepard that the recent discover- 

 ies in regard to the magnetic polarity of rocks and mountains, even 

 of those apparently destitute of iron, will explain the facts which I 

 observed on the Canaan mountain, without supposing a mass of iron 

 within it. But if I understand this polarity of a mountain, it affects the 

 needle more or less on every part of its surface : whereas it was af- 

 fected on the Canaan Mountain only within the space of a few square 

 rods of level ground near the top ; although I judged that the whole 

 top embraced hundreds of acres. Hence I infer that we must suppose 

 some local cause acting there on the needle. And why may not this be 

 native iron, since it was near that spot where veritable native iron was 

 knocked off from a bowlder ? If this be a reasonable supposition, it 

 would certainly be very interesting to have it confirmed; since native 

 iron, (except the meteoric,) is one of the rarest of minerals. 



One mile north of the village of Worcester, an excavation was 

 made several years ago in the mica slate in search of silver, &c. as 

 already described in the first part of my report. It is impossible to 

 ascertain at present how wide is the vein that was explored : but the 

 minerals thrown out, and lying around the opening, are arsenical 

 pyrites, carbonate of iron, and galena. Sometimes the arsenical iron 

 is in distinct crystals in quartz ; but I could not ascertain their form. 

 A little west of the village of Worcester, these same minerals occur 

 in the stone walls, along with the idocrase, rendering it probable that 

 this last mineral originated from that metallic vein. 



In Sterling, one and a half mile southeast from the village, are 

 two excavations in the same mica slate as that at Worcester ; and 

 large quantities of similar ores have been thrown out. Carbonate of 

 iron is most abundant ; arsenical iron less common. Blende, of a 

 cherry red color, is found there in considerable quantity ; galena also 

 occurs, which is argentiferous, according to Mr. C. T. Jackson. Sul- 

 phuret of iron exists in connection with the ores that have been men- 

 tioned, and pyritous copper also with the carbonate of iron. Before 

 the compound blowpipe the blende was reduced, and burnt with the 

 flame peculiar to zinc, throwing off the white oxide. Numerous 

 quartz veins traverse the carbonate of iron, and a considerable quan- 

 tity of red oxide of iron occurs in the quartz, probably proceeding 

 from the decomposition of the carbonate. The lamellae of this car- 



