322 



LIGNITES. 



tions of these deposits, with the errors which have 

 been committed respecting them, I may add a sketch 

 of what little is known with regard to the general 

 characters of each class or division. 



The lowest deposit, or that of the oolithe, which 

 may include all from the rnagnesian limestone upwards 

 to the green sand, is more frequently akin to coal 

 than to the woody lignites, though the latter substan- 

 ces occur also in various forms. In some places, it 

 exists in the strata in groups of different dimensions, 

 or in scattered fragments, or else in thin and partial 

 beds. In others, it forms regular beds of coal, of 

 various, and sometimes of considerable thickness; and 

 when these alternate with the shales, sandstones, and 

 limestones, of the series, the superficial aspect is so 

 much like that of the regular coal series, that it is not 

 surprising if it should have been mistaken for that 

 deposit. This coal however is generally, or perhaps 

 always, accompanied by woody lignites, commonly 

 in the state of charcoal, dispersed through the accom- 

 panying rock. In the example in Sutherland, one of 

 the beds is three feet or more in thickness, while 

 another does not exceed an inch. The animal re- 

 mains hitherto discovered are not numerous, but they 

 are thought to be marine ; and hence a distinction has 

 been attempted between this and the proper coal 

 series, respecting the truth of which I must enquire 

 hereafter. It is however probable that the supposed 

 existence of marine shells in this last, has generally 

 arisen from confounding it with the lignite coals 

 under review. If I name madreporites, ammonites, 

 belemnites, ostreae and echini, I need not proceed 

 with this list, since the shells to be expected are those 

 which belong to the calcareous series itself. 



The Lignite, as it occurs in the green sand, is said 



