Geological Society. 223 



tive age of this brown coal formation, a task extremely difficult, from 

 the almost total absence of shells, and the imperfect state of the 

 means of determining an epoch of formation by fossil plants. By 

 previous writers it has been assigned to the plastic clay of the Paris 

 basin ; but it appears to the author to possess no other character of 

 identity than the mineral composition of some of the beds, and the 

 occurrence of lignite, which prove nothing as to age. The amphi- 

 bious animal remains resemble those of the great fresh-water deposit 

 of CEningen ; but the few shells which occur, and the plants, are 

 identical in species with many of those occurring in the older fresh- 

 water beds of Aix in Provence. It seems to be very clear, that it is 

 an exclusively lacustrine deposit, and the organic remains, the only 

 evidence of age to be relied on where there is none from superpo- 

 sition of other beds, imperfect as they are, would seem to indicate a 

 more modern date than the plastic clay. The author states that a 

 distinguished geologist of Bonn has expressed his belief that it is 

 even older than the chalk ; but that although the opinions of that 

 experienced observer are entitled to great respect, he cannot recon- 

 cile the phsenomena described with anything known respecting the 

 secondary rocks. 



The determination of the age of this brown coal formation is of the 

 highest importance, as fixing the periods of eruption of the extinct vol- 

 canos of the Lower Rhine ; for the author of this paper shows, that the 

 trachytic tuff contains leaves of plants identical with those found in 

 the clay and sandstone deposits ; that extensive layers of trachytic 

 tuff are interstratified with the beds of the formation in many places j 

 and that in one situation a mass of basalt, thirty feet thick, lies upon 

 beds of coal thirteen feet in thickness. The conclusions which the 

 facts appear to the author to justify, are, that there existed a vast 

 fresh-water lake, in which the brown coal beds were deposited ; that 

 during that deposition volcanos burst forth at the bottom of the lake, 

 as they do now at the bottom of the sea ; and that a continuance of 

 volcanic action, or of elevatory force, raised the Siebengebirge after 

 the deposit had ceased, — perhaps at the very time when the basalt or 

 trap eruptions took place, since near the summit of the Mandeber^, 

 a columnar basaltic cone, there is a patch of brown coal beds at the 

 height of nine hundred feet above the surface of the Rhine. 



The last great formation, if it may be so termed, of this district, 

 lying upon the gravel in which the present bed of the Rhine is cut, 

 is that most remarkable deposit the Loess, a friable sandy loam, full 

 of existing species of land shells, without river shells, and without 

 plants, but containing bones of the Elephas primigenius and Rhino- 

 ceros tichorinus. It is found in detached masses, of vast thickness, 

 but without any signs of stratification, and sometimes at a height of 

 600 feet above the Rhine, and may be traced with scarcely any inter- 

 ruption from Bonn to Basle, a distance of 250 miles. The author 

 states that all the facts yet observed with respect to it, lead him to 

 conjecture that its origin may have been owing to the sudden burst- 

 ing of an extensive lake situated somewhere between Constance and 

 Basle, and that subsequent denuding causes have carried away the 



