1884. J 207 [Wads worth. 



of occurrence of the ores themselves. That the ores have been 

 subjected to mechanical and chemical action since the time of erup- 

 tion appears clear. This action has not only given rise to subor- 

 dinate mechanical deposits and to impregnations, segregations, and 

 minor veins, but has also been the means of the molecular re- 

 arrangement of much if not the whole of the ore. 1 



The iron ore of Cumberland, Rhode Island, has been shown by 

 the writer not to be a simple ore, but a rock composed chiefly of 

 titaniferous magnetite, feldspar and olivine. This ore appears to 

 be of an eruptive origin. 2 



The iron ore (magnetite) of Port Henry (Cheever Ore Bed) is 

 associated with and lies in a peculiar gneissoid rock composed prin- 

 pally of a clear, glassy, triclinic feldspar. This ore partakes of 

 the flexures of the gneiss and is in all respects to be regarded 

 as a sedimentary deposit ; but whether it is to be regarded as 

 a chemical precipitate or a cletrital accumulation the writer has at 

 present no opinion. The ore at times ramifies through the gneiss 

 in a way that only a chemical deposit or eruptive mass could, but 

 otherwise it has none of the characters of an eruptive. This 

 ramification then belongs to, or is the result of, chemical action, 

 yet it probably is not original, but a secondary result of chemical 

 agencies since deposition. Evidences of such action are com- 

 monly seen in the limestones in the vicinity, while its exciting 

 cause may have been the eruptive rocks (gabbros, etc.) which are 

 quite abundant in the vicinity. 



The ores in this part of the Lake Champlain region have been 

 cited as proofs by analogy that the Lake Superior iron ores were 

 also sedimentary deposits, but such arguments are deceptive, 

 since the deposits in the two districts in question have nothing in 

 common in their structure, their relations to the associated rocks, 

 or in their apparent origin, beyond the fact that both are magnetite 

 and both are associated with old crystalline rocks. 



In the vicinity of Balliurst boulders of iron ore (hematite and 

 jasper) were found in the bed of the Tete-a-gouche River which 

 closely resemble the associated hematite and jaspilite of the Mar- 

 quette District, Lake Superior. 



1 Bull. Mus. Comp. Zool., 1880, VII, 28-36, 66-76, 494, 495.— Proc. Bost. Soc. Nat. His- 

 tory, 1880, XX, 470-479. 



2 Bull. Mus. Comp. Zool., 1881. vn, 183-187.— Proc. Bost. Soc. Nat. Hist., 1881, xxi, 

 195-197— Lithological Studies, 1884, pp. 75-81. 



