November, 1841.] 119 



granite, as in Rhode Island, Massachusetts and Virginia, on the 

 older members of the secondary, as in the anthracite fields of Penn- 

 sylvania, or on the mountain or the " cliff"" limestone of the western 

 states, the coal series has every where been the product of a period 

 in the history of our planet which was highly prolific in vegetable 

 life, of which the remains were deposited on whatever member of 

 preceding formations was exposed in a condition to receive them. 



The anthracite of Rhode Island appears to have been subjected 

 not only to a high temperature, but also to intense pressure, and to 

 have been much comminuted by the friction of one member of the 

 formation sliding over another in the uptilting which the strata have 

 evidently undergone. The coal in all such cases being more tender 

 and friable than the sandstones, slates and limestones, becomes the 

 unguent in the joints of the stratification, and the results of its power 

 to facilitate the motions of the strata as they are partially folded up, 

 is, 1st, a pulverulent portion in contact with either the top or the 

 bottom rock of the bed ; 2d, a high polish imparted to some of the 

 sliding surfaces of the more durable coal ; 3d, an irregularity in the 

 thickness of the coal beds, the indentations of the upper and lower 

 rocks being not unfrequently found opposite to each other, forming 

 thick places in the coal seam, and containing much of the broken 

 material which has been displaced from the parts where the promi- 

 nences of the rocks come nearly in contract, and almost shut up the 

 seam. 



Prof. Johnson adverted to the fact that for reasons stated by the 

 geologists of Rhode Island and Massachusetts, viz. the great amount of 

 drift or diluvial matter with which all parts of this coal formation 

 have been covered over, the limits of the coal trough have not hitherto 

 been traced with much precision. 



Within the city of Providence, the strike of the beds is a little to 

 the east of south, and the dip of course to the north of east. The 

 mining operations are in general very troublesome and expensive, 

 on account of bein<r carried on below water level, and through a 

 thick stratum of loose earth and gravel. Very little of the coal 

 hitherto obtained has been of merchantable quality. 



