No. 4. — A 3ficroscopical Study of the Iron Ore, or Peridot itc, of 

 Iron Mine Hill, Camheriaml, liliodc Island. By ]\I. E. AA'ads- 

 WORTII. 



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

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

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

 oi'o of iron, but rather fragments of a basic eruptive rock containhig 

 much iron. Sections were accordingly made which revealed its true 

 character. 



The formation was described by Dr. Charles T. Jackson in his report on 

 the Geological Survey of Rhode Island in 1840. He states that Iron 

 Mine Hill " is a mountain mass of porphyritic magnetic iron ore, 462 

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

 adjoining meadow. From these measurements, which were made over 

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

 that there are G, 342,330 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 chemical com- 

 position in comparison with that of the iron ore, which we know to 

 have been thrown up with the serpentine, occumng on the estate of ^Ir. 

 Whipple, and the fact that the ore at Iron Mitie Hill is accompanied by 

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

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



He gives as the result of his chemical analysis of the " Poi'phj-ritic 

 Iron Ore from Iron Mine Hill, Cumberland," the following (/. c, p. 53) : — 



SiOa 23.00 



AloOj 13.10 



FePj 27.G0 



Feb 12.40 



MnO 2.00 



MgO 4.00 



TiO, 15.30 



H2O and loss 2.00 



Total, 100.00 



VOL. VII. — NO. 4. 



