STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 147 



shows that here one has a good example of pond-filhng. The same 

 relations are seen on the left bank of the Rhine near Oedenberg and 

 Liessen ; at the latter, Blatterkohle attains its greatest thickness, vary- 

 ing from 3.8 to 16.5 meters. The total area of rich Blatterkohle 

 barely exceeds one square mile. 



Alum brown coal, like Blatterkohle, is confined to the more 

 southerly portions of the region containing the Oligocene basins ; 

 it is found especially on the Hardt near Putzchen and Spick on the 

 right, and near Godesberg and Friesdorf on the left side of the 

 Rhine, where it is associated with layers of ordinary and lignite-like 

 brown coal. The Hardt area is about 10 by 4 kilometers and in- 

 cludes the Rott deposit already referred to. The coal there is 3 to 

 4 meters thick, mostly earthy brown coal and so pyritous that the 

 ashes are used in the alum industry. Midway, is a meter of lignitic 

 brown coal, composed largely of prostrate stems. One of these, a 

 conifer, was 1,600 years old, that being the number of annual rings. 

 But erect stems are by no means rare; one mine near Bleibtreu 

 yielded 35 such stems in a space of 10 acres, the diameter varying 

 from 0.78 to 2.82 meters or about 9 feet. Pyrite replaces or pene- 

 trates much of the stems and roots. This lignite on drying becomes 

 black and changes into a typical Pechkohle. The plants are mostly 

 conifers and palms. The relations of the coals are shown in a section 

 measured near Friesdorf, thus : Loam and river drift, 5.2 ; brown coal 

 and alum clay, 0.94; clay and bituminous wood, 1.26 to 1.57; brown 

 coal (lignite), 0.16; bituminous clay, 0.31; brown coal and lignite, 

 0.16; gray pyritous clay with lignite, 1.57; brown coal, 2.51; black 

 alum clay, 1.57; Blatterkohle, 0.47; lignite, 0.47; earthy brown coal, 

 0.94 ; Blatterkohle, 0.63 to 0.94 ; earthy brown coal, 0.47 ; Blatter- 

 kohle, 0.63 to 0.94. 



The association of Blatterkohle and pyrite seems, from Heusler's 

 sections, to be very intimate at most localities. Nineteen species of 

 plants have been recognized at Friesdorf, a large part of them belong- 

 ing to genera well represented in swamp floras. Erect stumps are at 

 FiJssenich and Stockheim. 



Alumkohle and Blatterkohle become rare northward and earthy 

 brown coal, like the Formkohle of Sachsen, is the usual type. Lig- 



