I9II.] STEVENSON— FORMATION OF COAL BEDS. 61 



Degousie, in sinking artesian wells at Venice, found beds of lignite 

 and carbonaceous clays at 40, 60, 100 and 120 meters from the 

 surface. 



\'on Giimbel,''' perplexed by the contradictory results presented 

 in memoirs, undertook a series of systematic studies, covering all 

 phases of the subject. His study did not concern itself with chem- 

 ical or technical matters and had little reference to botanical rela- 

 tions. At the outset, it deals only with questions relating to the 

 constitution of coals; it begins with examination of peat-like sub- 

 stances and advances, step by step, to anthracite and graphite ; it 

 ends with a discussion of the mode in which coal beds accumulated. 

 In breadth of scope, this study excelled that by any predecessor ; in 

 compactness and precision of statement the memoir has rarely been 

 excelled. Much of the earlier portions bear directly on questions 

 respecting the transformation of vegetable matter into coal, a sub- 

 ject to be considered in a later part of this work; but some of his 

 observations are so closely connected with the final part of his dis- 

 cussion that they cannot be neglected. 



The method of investigation by means of thin sections did not 

 commend itself to v. Giimbel, who preferred the method proposed 

 by Franz Schultze. The broken coal was treated first with potas- 

 sium chlorate and strong nitric acid, and afterward with ammonia, 

 in order to separate the particles and to make the transparent por- 

 tions more readily available. Absolute alcohol completed the prepa- 

 ration by removing coloring matters. He gives specific directions 

 as to the use of the reagents and warns against the possibilities of 

 error in the study. 



This investigation led him to recognize that the whole series from 

 peat to anthracite is continuous and of similar origin. All of the 

 members are made up of combustible materials. " Stone coal con- 

 sists, apart from the earthy admixtures, of parts of plants, which, 

 changed into a coaly substance, have taken up into their empty 

 spaces, as well as into the intervals between the plant debris, a 

 humin-like or ulmin-like substance ( carbohumin ) which was origi- 



°' C. W. V. Gumbel, " Beitrage zur Kenntniss der Texturverhaltnisse dcr 

 Mineralkohlen," Sitcuiigs. Bcrichfcn dcr k. buyer. Akad. d. Wissenschaften. 

 Mafh.-Pliys. Klassc. 1883, pp. 113 et seq. The citations are from pp. igo-212. 



61 



