14 INTRODUCTION. 



influences. This is, however, almost never the case. It commonly happens 

 that layers of very different character alternate in the seams, and as they 

 are suitable for different economic purposes, they are kept separate when the 

 c-oal is removed from the mine. The single layer too is seldom of the same 

 composition throughout, but is very frequently made up of thin alternating 

 secondary layers, of dull, for example, and of highly lustrous coal. Further, 

 in many places, such as Upper Silesia, Zwickau, and St. Etienne, fibrous 

 (?bal is found in irregular nests, masses and strips breaking through and 

 traversing the other kind of coal, so that the whole assumes a highly 

 complicated structure, which varies from case to case and has been taken 

 into consideration in naming the different coals. Thus anthracite, which is 

 traversed by an unusual number of layers and strands of fibrous coal, is 

 termed sooty coal 1 , and as in such cases the parts of the seam which are of 

 like character were exposed to the like external influences, the difference in 

 detail must depend, as Goppert concludes, on the originally dissimilar 

 character of the material employed in the formation of the coal. This dis- 

 similarity we may ascribe with Goppert to the association of different 

 species of plants in varying proportions, or with Grand' Eury 2 to the 

 bringing together of parts of plants, in which specific difference had 

 less effect than the varying degree of decay and maceration in each case. - 



To increase the probability of all these conclusions, Goppert 3 also set 

 himself to test them by the method of experiment. Similar attempts had 

 been already made by Wiegmann, and after him by Petzholdt 4 . Un- 

 fortunately they were none of them thoroughly and logically carried out. 

 Goppert experimented with portions of plants in closed vessels with water 

 at a temperature of 60-80 R., and for a period extending over several 

 years, and he states that his material formed at length a brown coal-like 

 mass. Lustre and black colour were only obtained by addition of a small 

 quantity of sulphate of iron. Coarse cloth which covered the cylinder in a 

 cloth-manufactory, after being many years in use, was found to be converted 

 into black coal with conchoidal fracture. Unfortunately none of these 

 substances was examined chemically; we do not know therefore how far it 

 could be compared with true pit-coal. 



From all that has been ascertained through the efforts of different 

 observers, there can be no longer any doubt that layers of coal have been 

 formed of fragments of plants and of vegetable detritus under water ; and 

 therefore we have long seen the necessity of studying analogous processes 

 going on before our eyes at the present time under similar conditions, 

 namely those which result in the formation of peat and brown coal. 



The formation of peat is everywhere dependent on the presence of 



1 Mietzsch (1;. - Grand' Eury (2;. " Goppert (15). * Petzholdt (1). 



