208 Dr. Mac Culloch on the Lignites. 



fectly bituminized. Thus, this confusion of character, no less 

 than the indefinite nature of lignite with respect to peat, com- 

 pletes that series of transitions by which the latter is connected 

 with coal. These remarks apply solely to those substances con- 

 sidered as minerals. The geological distinction arising from 

 position, is sufficiently marked. 



In enumerating the different substances to which the term lig- 

 nite has been most commonly applied, it becomes now necessary 

 to add coal, without which, we should exclude some of the most 

 important deposites of this combustible. The other varieties which 

 have been enumerated by mineralogists, are brown coal, or Bovey 

 coal, surturbrand, jet, and Cologne earth, or pulverulent lignite. 

 Of these, however, the three first are not absolutely defined 

 species ; since, among various specimens of each, there are found 

 differences sufficient to show that they tend to graduate into each 

 other. Thus Bovey coal, as it becomes darker and more bitumi- 

 nous, passes towards surturbrand ; while, between this species and 

 jet, the distinctions are often very difficult to make. If those 

 lignites which are here ranked with Cologne earth, are not always 

 powdery, they are at least sufficiently tender to be easily reduced 

 to that state. To these we ought to add, the casual specimens, 

 of no decided character, which occur in many parts of the various 

 strata; with the fragments of vegetables, the fruits, and other 

 remains of a similar nature, that are generally described among 

 the organic substances. The origin and theory of the whole is 

 similar ; but as there is nothing in these of sufficient importance 

 to require a separate detail, they may be omitted from the pre- 

 sent considerations, as casual fossils in the strata, of which the 

 description belongs to the history of these rocks. 



There are three obvious situations, sufficiently distinct in geo- 

 logical circumstances, in which lignite occurs ; namely, in alluvial 

 soils, under stratified rocks, and connected with rocks of the trap 

 family. But these are insufficient for the present purpose ; as 

 the importance of some of the deposites requires that they should 

 be distinguished by their more rigid geological connexions. 

 Though I here omit the coal which occurs in the red marl, it ought, 



