Mr. Horner on the Geology of the Environs of Bonn. 467 



sequent denudation. At Friesdorf the clay and lignite beds rest imme- 

 diately upon the ends of highly inclined strata of grauwacke. I have 

 already noticed, p. 442. the alternation of trachyte tuff with the beds of the 

 brown-coal formation ; and at p. 441. I have described the occurrence at 

 Quegstein of trachyte tuff lying upon sandstone. I have also said, p. 443. 

 that basalt occurs in connexion with the brown-coal formation : the place 

 where this has been most distinctly seen is at Utweiler, on the north-eastern 

 border of the district, about four miles from the centre of the trachytic and 

 basaltic eruptions of the Siebengebirge, but situated in a valley between two 

 knolls of basalt, the Rother Hardt, nearest to it, and the Hinzberg, not very 

 far off. I visited this place in 1832 with Professors Noggerath and Mit- 

 scherlich, to see the workings in a new shaft which had been sunk to obtain 

 the coal. The former has lately published in Karsten's Archwfur Bergbau, 

 &c., an account of his observations, together with some subsequently made 

 by M. Augustus von Strombeck, on this occurrence of basalt in the lower 

 ground. M. von Strombeck drew up the following account of the different 

 beds sunk through in the new shafts : 



Ft. hi. 



1. Soil 2 6 



2. Loess 9 5 



3. Basalt 30 6 



The upper part consists of globular masses in some degree decomposed ; then 

 comes a dark gray compact basalt, containing olivine, augite, and magnetic iron 

 ore, but not regularly columnar. 



The lower part of the mass is formed of 



4. A compact bluish gray argillaceous stone, a decomposed basalt or tuff, similar to 



what usually accompanies volcanic masses 1 3 



5. Here begin the brown-coal beds properly so called ; an indurated clay of a black 



colour from a mixture of coal, which splits into prisms about three inches long, 

 and from eight to ten lines in diameter, the interstices filled with crystallized dolo- 

 mite ; a structure probably occasioned by the heated mass of basalt covering it 10 



6. Dark-coloured clay, containing much coaly matter 'and pyrites, but neither slaty 



nor columnar 6 



It is remarkable that this bed should show no indication of that columnar 



structure which is so marked in the beds which lie immediately above and 



below it. A similar fact has been observed in the Meisner. 

 Then come the lignite beds, consisting of 



7. Black pitch coal, separating into prisms of from an inch to an inch and a half in 



diameter, standing perpendicular to the face of the basalt bed, with the inter- 

 stices lined with crystallized dolomite 1 2 



This passes gradually into 



8. A small coal 4 



