BQUIVALENTS. 



61 



TABLE OF EQUIVALENT STRATA. 



Cr?^ I cannot deem worthy of imitation the numerous sub- NumeroBa 



^ _ _ European 



divisions of some Europeans, into from fifty to ninety strata, strata ab- 

 I consider Bakeweli the only author, well known in America, 

 who has presented us with a rational system of generalization. 

 The labors of A. Brongniard, Conybeare, De La Beche, and 

 others, claim our high esteem ; but not our imitation. In this 

 table, i refer to the equivalents of Bakeweli chiefly. But I 

 consider my duty well performed, as the author of a text-book, 

 if I refer accurately to any good foreign authority, even with- 

 out citing the name.* 



1. Granite. Same in Europe — the slaty kind often called PHmitiTe. 



gneiss, 



2. MicA-sLATE. Same in Europe. 



3. Hornblende rock. Same in France, &c. 



4. Talcose slate. Same in Europe, with subdivisions stea- 



chist and chlonite slate. 



5. Granular (QUARTZ. Same of some, quartz rock others. 



6. Granular lime-rock. Crystalline lime-stone, j^rimary 



lime-stone, statuary marble. 



7. Argillite. Same of some ; slate, clay-slate of others, '^f^^^'^'^"- 



and argillaceous shistus of others. Alum-slate of some ; 

 but the alum-slate is found in argillite, and in 1st, 2d, and 

 3d graywacke. Flinty slate of some is always a bed or 

 alternating layer in argillite. Inclined graywacke slate Inclined 

 -is the uppermost side of argillite, containing an increased 

 proportion of silicious grains and spangles of mica or talc. 



8. First graywacke. Same. But as the English confound Thrausim 



several rocks under this name, it may be said to be strict- ed wfS!"*" 

 ly equivalent to the French name, thrausma, fragmented 

 rocks. 



« I intend to pursue this subject much farther, in a future publication. 



