Bibliography. 187 



Near Newport, on the sea shore, there is a large vein of quartz 

 thirty feet wide, cutting through slaty rocks. In this vicinity are nu- 

 merous beds of anthracite from one foot to three feet in thickness, 

 and the slate rocks of carbonaceous clay containing them are charged 

 with myriads of fossil plants. The intrusion of granite has here 

 produced the usual appearances of hardening — vitriiication and sco- 

 riae, and there are beds of intruded serpentine at Willow Grove, near 

 Fort Adams. 



With the geology of this island we were early familiar, and trav- 

 ersed it many times with the late Col. Gibbs, in 1807, and we are much 

 impressed with the correctness of Dr. Jackson's views of the conglome- 

 rate at Purgatory, two miles east of Newport. The pebbles of hard 

 quartz are from an inch to a yard long; they are all ovoidal, and lie with 

 their longest diameters parallel to each other, as if swung around by 

 a strong current, like ships at anchor ; the surfaces of the pebbles 

 are polished as if by long abrasion of water and sand, and they are 

 firmly cemented by a finer paste of a similar nature, but apparently 

 fused, their surfaces being often covered with an infinity of minute 

 crystals of magnetic iron ore, which often also forms a part of the 

 cement. We have remarked also that the slaty graywacke in the 

 same vicinity, has similar crystals, often distinctly octahedral, and if 

 with Dr. Jackson, we attribute the one to the operation of fire, we 

 must assign the same origin to the other. There is a rent in this 

 conglomerate from eight to ten feet wide, and from thirty six to forty 

 four feet deep. This fissure was once occupied by a trap dyke, most 

 of which has been washed away by the sea, which, especially in eas- 

 terly storms, roars and dashes into this fissure. The power that up- 

 hove the rock, has cracked the pebbles accurately in two, like plumbs 

 divided by a knife in a pudding.* In Portsmouth, near the north 

 end of Rhode Island, there are important strata of anthracite which 

 were once extensively wrought, but the exploration was given up about 

 fifteen years ago. The strata were stated to be three in number, and 

 varying from two to twelve feet in thickness. 



By Dr. Jackson's analysis, a clean specimen of this coal gave wa- 

 ter and volatile matter 10, carbon 84.5, dark red ashes 5.5. A spe- 

 cimen of the rusty coal, gave water and volatile matter 7, carbon 

 77.0, dark purple red ashes 16 — consisting of silex 7.4, oxide of iron, 

 alumina, manganese, and a little lime, 8.0. This is a valuable coal, 

 as we have had occasion to know from experience ; and we stated in 

 Vol. xiii, p. 78, of this Journal, the quantity of inflammable gas 



* The name Purgatory, popularly applied to this fissure, is said to have arisen 

 from a lover's leap having been made across the gulf to please and win a fai^ 

 maiden ; and the fortunate lover at once declared his transit from purgatory to par- 

 adise. 



