SCIENCE. 



369 



part, gives still greater reason for this belief." (7. c, pp. 



52. S3-) , 



He gives as the result of his chemical analysis of the 

 " Porphyritic Iron Ore from Iron Mine Hill, Cumber- 

 land," the following (I. c, p. 53): — 



SiO a 23.00 



AUOj 13. 10 



Fe,0 3 27.60 



FeO 1 2 . 40 



MnO 2.00 



MgO 4.00 



TiO a .. 15.30 



H 2 and loss 2 . 60 



Total 1 00. 00 



In 1869 the Rhode Island Society for the Encourage- 

 ment of Domestic Industry published a report relating to 

 the coal and iron in Rhode Island, from which we glean 

 the following. The iron ore is regarded as practically 

 inexhaustible, the mass at Iron Mine Hill visible above 

 drainage being estimated at two millions of tons. 



" It is also conceded, as regards quality, that the Cum- 

 berland ore is free from sulphur and phosphorus, the 

 most common and worst impurities, and that it contains 

 manganese, the most prized of all the elements found in 

 connection with iron. For these reasons the Cumber- 

 land ore is sought by manufacturers at a distance, to mix 

 with softer ores and improve their quality, and is now ex- 

 ported from this State for that purpose." 



It seems that this Iron Mine Hill ore was employed in 

 1703, mixed with the hemitite of Cranston, R. I., for the 

 casting of cannon. The work was done at Cumberland, 

 and, in part at least, " the cannon used in the celebrated 

 Louisburg expedition, in 1745," were cast from these 

 ores. The manufacture was abandoned in 1763, owing 

 to an explosion of the furnace, by which the proprietor 

 was killed. 



During the administration of John Adams the same 

 ores were also used for the manufacture of cannon. It 

 seems that the Cumberland (Iron Mine Hill) ore was 

 employed in the manufacture of charcoal iron at Easton, 

 Chelmsford, and Walpole, Mass., as late as 1834. " The 

 Cumberland ore, mixed with equal quantities of Cranston 

 hematite or bog ore, produced, for a long period, a char- 

 coal iron unsurpassed in this country. . . . The Cumber- 

 land ore contains an uncertain percentage of titanium, 

 which, while it improves its quality, helps make it refrac- 

 tory. The ore is porphyritic, the magnetic oxide being 

 associated with earthy minerals, principally feldspar and 

 serpentine." It would seem that in 1869, and before, 

 the ore was largely shipped to Pennsylvania to mix with 

 other ores. 



A letter of Professor R. H. Thurston, published : n 

 this report, states : "The Cumberland iron ore is of the 

 kind known to mineralogists as 'ilmenite;' among met- 

 talurgists as ' titaniferous magnetic ore,' and iron manu- 

 facturers, on account of its peculiar value for producing 

 steel, would term it a 'steel ore." . . . The Cumberland 

 ore is conveniently located and of inexhaustible extent ; 

 it is perfectly free from noxious elements, though some- 

 what refractory ; it will furnish a very strong iron or a 

 most excellent steel ; it can be smelted within the State 

 at a profit ; it can be made directly into steel at a much 

 greater profit ; steel made from it will bring the highest 

 prices in the market." 



Professor Thurston states that the mean of various 

 analyses made of this ore is about as follows : 



Si0 3 22.87 



Al a 3 IO.64 



Fe '- ,0:t i , , 8S 



MnO 2.05 



CaO 0.65 



MgO 5.67 



TiO 9.99 



Zn 0.20 



H-,0 and loss 3.05 



Total 100.00 



The ore on one side of the hill, where it has been most 

 extensively quarried, shows a dark, somewhat resinous 

 groundmass, holding large striated crystals of feldspar. 

 The resinous lustre and greenish-yellow color, as ob- 

 served under the lens, are caused by the presence of 

 olivine. The olivine becomes more strongly marked on 

 the slightly weathered surfaces seen on the faces of the 

 quarry. Under a lens of high power, the olivine shows 

 clearly on the fresh fractures. The olivine in weathering 

 decomposes to a yellowish and reddish-brown ferruginous 

 powder, leaving the other constituent of the rock, the 

 magnetite, well marked. The magnetite decomposes 

 more slowly, and forms an incoherent mass after the de- 

 cay of the olivine. The rock gelatinizes with hydroch- 

 loric acid, and yields a titanium reaction. A fragment 

 allowed to stand a day or two in weak hydrochloric acid 

 yielded gelatinous silica copiously. 



A section made with special reference to the feldspar 

 crystals shows large porphyritic crystals of the latter en- 

 closed in a mass of magnetite and olivine. 



The magnetite forms irregular, more or less connected 

 masses, making a sort ot sponge-like structure. Its 

 rounded and irregular cavities are filled with olivine, 

 which also occupies the interspaces between the magne- 

 tite masses. The olivine is in rounded forms, which 

 sometimes show one or more crystal planes. It is cut 

 through by numerous fissures, that usually show a fer- 

 ruginous staining along their sides. The olivine also 

 holds grains of the magnetite. Except the fissuringand 

 ferruginous staining, the olivine is comparatively clear, 

 and shows little signs of alteration. 



The plagicclase feldspar shows well-marked lines of 

 cleavage and fracture, and is somewhat kaolinized along 

 these lines. It contains a few irregular flakes of biotite 

 together with grains of olivine and magnetite. 



The order of crystallization appears to have been, first 

 the magnetite, then the olivine, and lastly the feldspar. 



This rock is similar to the celebrated iron ore of Taberg, 

 Sweden, as described by A. Sjoren in the Geologiska 

 Fbreningens Forhandlingar (1876, III. 42-62 ; see also 

 Neues Jahrbuch fiir Mineralogie, 1876, 434, 435.) The 

 Taberg rock has been worked as an iron ore tor over 

 three hundred years. This Swedish ore is called by 

 Sjoren " magnetite-olivinite." 



The feldspar is confined to the peridotite found on one 

 side of the hill, where the peridotite passes into a compact 

 greenish-black rock, showing patches of serpentine and 

 grains of magnetite. From this fact it seems necessary 

 to regard the feldspar as abnormal and local in the rock, 

 which in general is composed of olivine and magnetite 

 or their alterative products. 



The structure remains about the same in the non- 

 fcldspathic portions as it is in those before mentioned as 

 holding feldspar. But the olivine is entirely changed to a 

 greenish serpentine which shows beautiful fibrous polari- 

 zation. The serpentine retains the form of the olivine 

 grains, their inclusions, and the network of fissures before 

 mentioned. In some of the sections considerable car- 

 bonate was seen, presumably dolomite. In one section 

 part of the olivine grains, especially towards their interior, 

 remained unchanged, but on their edges they were al- 

 tered to serpentine. Another change was observed here : 

 the formation of secondary crystals of irregular outline 

 that belong probably to actinolite. Some are elongated 

 and narrow ; other are short and broad, traversed, by- 

 cleavage planes. They evidently belong to the mono- 

 clinic system. 



The origin of this rock could not be told from its 

 field relations, as its contact with any other rock could 



