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



to the south of the town of Bergheim, between Cologne and Juliers, a stretch of about thirty miles ; 

 and Professor Noggerath informs me that he has traced tlie lignite beds at intervals from Bergheim 

 to Aix la Chapelle. The breadth of the plateau varies from three to five miles. Its greatest ele- 

 vation is about 200 feet above the plain on the eastern side ; and from the foot of the plateau near 

 Briihl to the Rhine, a distance of about five miles, there is a fall of fifty feet*. These two districts, 

 on the right and left banks of the Rhine, are the chief deposits ; but the formation occurs at several 

 places further south, on both sides of the river, and also within the volcanic regions of the Sieben- 

 gebirge and Lower Eifel. 



A. The Siliceous Deposits. 



The lowest member of the formation seems to be the loose siliceous sand ; 

 with this is associated, and generally covering it, a sandstone of various de- 

 <*-rees of coherence, sometimes so friable as to be easily rubbed between the 

 fingers, at others as compact as a granular quartz rock. At Tanzchen and 

 Quegstein, in the valley above Konigswinter, all these varieties may be seen 

 together. Here also are found thick beds of a quartzose conglomerate, the 

 pebbles of which are for the most part small, but sometimes as large as a 

 pigeon's egg, and so associated with the fine-grained quartzose rock, that 

 specimens may be obtained of both united, sometimes showing a gradual 

 transition from the coarse to the fine, at others a sharp line of separation. 

 In specimens no one could distinguish this sandstone conglomerate of fresh- 

 water formation from rocks of constant occurrence in the grauwacke and 

 older secondary strata. The conglomerate is traversed by yellow and brown 

 semi-opal, which occasionally assumes the mammillary structure of chalcedony, 

 and in which traces of vegetable structure may be detected. 



In the neighbourhood of Rott and Geistingen, on the right bank of the 

 Rhine due east of Bonn, there are found, associated with a thin leafy bitu- 

 minous lignite which has obtained the name of Papierkohle {Paper-coal), 

 laminas of a flinty substance, seldom above an inch thick, and usually accom- 

 panied with thin friable siliceous plates, earthy, and bearing some resemblance 

 to the Polierschiefer that is found in the brown-coal formation of the Ha- 

 bichtwald. Between the plates of the Papierkohle siliceous concretions, of 

 the form and size of beans, are sometimes found. 



B. The Argillaceous Deposits. 



These consist of beds of clay of various qualities and colours, according to 

 which they are used for making bricks, tiles, and pottery ; and some is sent 

 into Holland for making tobacco-pipes. In many places the clay is much 



* Von Dechen, Beschreibung des Kuhlen und Tummelhau in dem Briihler Braunlcohlenrevier, 

 in Karsten's Archiv., vol. iii. 1831. 



