224 Review of "Outlines of the 



whetstones, grindstones, &c. ; some varieties of a large 

 schistose structure are raised as flag-stones for paving ; 

 others, more finely laminated, as roofing slates." p. 333. 



These are the only rocks in which coal occurs sufficient- 

 ly pure, or abundant, to be profitably wrought. Carbona- 

 ceous matter, however, of inferior quality, and sometimes 

 used as fuel, is found in thin seams, in other deposites. It 

 may be useful to present a view of the several formations 

 in which coal, or carbonaceous matter has been found. 



1 Alluvial. — This furnishes peat ; which is formed by 

 the accumulation o{ sphagnum palustre, or other mosses, or 

 maritime plants : the lower parts of the mass gradually 

 undergoing a change into peat, and even into a substance 

 not differing essentially from jet. 



2. Diluvial.- — Contains beds offossil wood, passing, by a 

 series of gradations, into jet. 



3. Basaltic formation, or Newest Floetz Trap. — In Ire- 

 land and Germany, a species of lignite, similar to that just 

 mentioned, is associated with this formation. 



4. Plastic Clay. — The coal in this formation occurs in 

 beds, is obviously of vegetable origin, and is of little 

 value. 



5. Sand immediately below the Chalk. — This has all the ap' 

 pearance of an imperfect coal formation ; the coal existing 

 in the form of fossil wood, and in distinct beds ; but it is 

 very poor. 



6. Oolitic Series. The Kimmeridge Clay embraces bi- 

 tuminous shale, which is sometimes used for fuel ; and the 

 sands, resting on the lias, present regular beds of workable 

 coal. 



7. Newer Red or Saliferous Sandstone. On the conti- 

 nent of Europe, this rock contains thin seams of coal; but 

 they have not been noticed in England. 



8. The Great Coal Formation. This is the next deposite 

 of coal in the descending series. 



9. Transition Slates. (Gray Wacke Slate, &lc.) Some- 

 times beds of anthracite are contained in these rocks, as in 

 Devonshire. A fine example exists also in Rhode Island 

 in this country. 



10. Mica Slate. This and other primitive rocks furnish 

 beds of anthracite and plumbago. 



That coal, with the exception of the non-bituminous va- 

 rieties, is of vegetable origin, seems now to be generally 



