214 Dr. Mac Culloch on the Lignites. 



expected are those which belong to the strata in which the lig- 

 nite lies. 



The lignite, as it occurs in the green sand, is said to exist rather 

 in heaps of fragments than in proper beds, but the descriptions of 

 individual cases are imperfect and unsatisfactory. In the Isle 

 D'Aix the accompanying substances are sands, marls, and cherty 

 flints, with quartz, agate, pyrites, and resinous substances. The 

 wood is that of dicotyledonous plants, and it is said that no palms 

 have been found. This wood is sometimes silicified, at others 

 fibrous, or in the state of jet. Fuci also are said to occur, and the 

 shells are all marine, consisting of nautilites, pectinites, gryphites, 

 and others. With respect to these fossils, the same general rule 

 may be applied as in the former case. 



The deposites of lignite found in the strata which succeed to the 

 chalk, or in the tertiary or fresh- water formations, have recently 

 experienced considerable attention, particularly in France ; though 

 our general knowledge of them is still necessarily limited. The 

 period of this deposite is sufficient to distinguish them from those 

 which belong to the inferior strata, or to the alluvial formations ; 

 and their origin and causes are similar to those of the animal 

 remains in the same situations. It is unnecessary to say that the 

 lignite may occur in any of the strata that belong to this series, 

 and equally unnecessary, here, to give more than this general in- 

 dication, as the peculiar cases must be sought in local descriptions. 



Besides the several mineral substances, or rocks accompanying 

 them, which need not now be repeated, they are, in different 

 places, found attended by quartz, agate, calcareous spar, sulphate 

 of strontian, pyrites, and hydrated iron, together with amber, and 

 imperfectly-bituminized resins, such as those of Bovey and 

 Highgate. 



The lignites themselves are sometimes fibrous and woody, while 

 at others they pass into jet, and even into coal, being further occa- 

 sionally silicified. Leaves and fruits occur, together with woody 

 stems ; and these can be referred to both dicotyledonous and mo- 

 nocotyledonous plants. The hitherto imperfect arrangement of 



