

No. 4:. ~~ A Microscojncal Sttuly of the Iron Ore, or Peridotite, of 

 Iron Mine Hill, Giiviberland, Rhode Island. Bij M. E. Wads- 



WOKTII. 



The attention of the writer was first particularly called to tliis forma- 

 tion by some specimens presented to him by Mr. H. 11 Metcalf in the 

 spring of 1880. These did not appear to the writer to be any common 

 ore of iron, but rather fragments of a basic eruptive rock containing 

 much iron. Sections were accordingly made which revealed its true 

 character. 



The formation was described by Dr. Charles T. Jackson in his repoi't on 

 the Geological Survey of lUiode Island in 1810. lie states that Iron 

 Mine Hill *' is a mountain mass of porphyritic niagnctic iron ore, 4G2 

 feet iu length, 132 feet in width, and 104 feet in height above the 

 adjoining meadow. From these measurements, which were made over 

 only tlie visible portion of this enormous mass of iron ore, it will appear 

 that there arc G,312,33G cubic feet of the ore above natural drainage. 

 . . . Its specific gravity is from 3,82 to 3.88. . . . This ore is remark- 

 able both on account of its geological situation and its miueralogical 

 and chemical composition. It appears to have been protruded through 

 the granite and gneiss at the same epoch with the elevation of numerous 

 serpentine veins which occur in this vicinity. This will appear the 

 more probable origin of this mass, when we consider its eliemical com- 

 position in comparison with tliat of the iron ore, which wc know to 

 have been thrown up with the serpentine, occurring on the estate of Mr. 

 Whip})lc, and the fact that the ore at Iron Mine Hill is accompanied by 

 serpentine mixed with its mass in every part, gives still greater reason 

 for this belief." (/. c, pp. 52, 53.) 



Ho gives as the result of his chemical analysis of. the *' Porphyritic 

 Iron Ore from Iron Mine Hill, Cumberland," the following {l. <\, p. 53) ; — 



SiOa 23.00 



A1,0, 13.10 



Fc^O, 2 7. GO 



FcO 12.40 



MnO 2.00 



I\IgO 4.00 



TiO^ ir^.30 



H^O and k)ss 2. GO 



Total, 100.00 



vol,, vir. — ISO. 4. 





