6 Johnson and Warren — Geology of Rhode Island. 



was about the same as at present. He also expresses his belief 

 that not over six inches have been removed by erosion since. 

 Several sketches of the hill as it appeared in 1883 and a map 

 of the bowlder train accompany the article. 



At a later date, the same writer expresses the belief that 

 the rock might continue downward to an indefinite depth and 

 to the north and south, beneath the drift, in the direction of 

 its strike, an opinion shared by the present author. 



Professors F. D. Adams, J. H. L. Vogt, J. F. Kemp, and 

 Richard Beck, in the publications given after their names at 

 the end of this paper, all mention the cumberlandite as a 

 probable segregation from a gabbroitic stock and class it with 

 the similar rock from Taberg, Sweden and other rocks of like 

 origin. 



General Description of the Iron Mine Hill and adjacent 

 Formations. — The cumberlandite is a dike like boss of igneous 

 rock which consisted originally of olivine (hyalosiderite), mag- 

 netite, ilmenite, labradorite, and accessory spinel. 



From surface indications and magnetic observations it 

 appears to have a rudely elliptical cross section with a 

 major axis of about 1200 ft. and a minor axis of from 

 500 to 600 ft. The direction of the major axis lies nearly 

 north and south. From the position of bowlders in the drift to 

 the west of the hill, it seems likely that the mass may extend 

 under the drift to the north farther than is indicated by its 

 present outcrop. There may also be a southward extension 

 of the mass, but the nearest outcrops of adjacent rocks on the 

 north and south certainly limit the length to a maximum of 

 about 2500 ft. and probably a much less smaller figure is the 

 correct one. That the maximum width is much greater than 

 the figure given seems improbable from considerations that 

 will appear later. 



The cumberlandite is now exposed in an unaltered condition 

 at only one point on the western side of the main ridge, a 

 little below the middle and a few feet below the top. With 

 reference to the probable dimensions of the rock mass as 

 indicated above, the unaltered portion is very nearly central. 

 It occupies an area of from 300 to 400 square feet and passes, 

 with a relatively narrow transition zone, into the more or less 

 altered t} 7 pes which constitute by far the greater portion of 

 the present hill. 



The Hill rises rather abruptly to a height of about 100 ft. 

 above the surrounding country, and of about 60 ft. above its 

 own base. Its upper portions, except where altered by quarry- 

 ing operations, consist of rounded, irregular prominences hav- 

 ing a dark brown to black color. Their rounded outlines are 



