Mineral Contents. 275 



p 



The proximity of granite explains satisfactorily the very great 

 irregularity in the position of the graywacke slate in Newport. 



From the various statements which I have made in relation to the 

 geology of Newport and its vicinity, it will be obvious that it is very 

 rare to find so many objects interesting to geological curiosity brought 

 within so narrow a compass. 



As to the thickness of the graywacke formation, I am very much 

 in the dark. I am inclined, however, to believe that its perpendicu- 

 lar thickness must be rather small. The want of lofty hills in this 

 formation, and the marks of powerful abrasion every where exhib- 

 ited, both in the loose fragments and in occasional outliers, have im- 

 pressed me with the idea that it was once far more extensive than at 

 present. It might not, indeed, have covered all the space that now 

 intervenes between its several tracts: but I see no reason why 

 much of that space might not have been occupied by it : although I 

 confess that this opinion is little more than hypothesis. 



Mineral Contents. 



By far the most interesting and important mineral in the gray- 

 wacke formation is anthracite. Its most abundant and best known 

 locality is in Portsmouth, near the northern extremity of Rhode 

 Island. It was explored there somewhat extensively near the begin- 

 ning of the present century ; and Dr. Meade says, that the vein then 

 wrought, was 1 4 feet wide; and " with only fifteen workmen, they' 

 can raise at present from 10 to 20 chaldrons of coal per day, besides 

 keeping the mine free from water ; from which they suffer little in- 

 convenience."* He speaks of the bed of coal as " not horizontal or 

 vertical, but forming an angle of about 75." 



* Bruce's Mineralog-ical Journal, January, 1820, p. 84. 



