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



APPENDIX— March, 1836. 



See Page ^SS. 



I. Page 433. 



M, VAN DER Wyck makes the mean height of the surface of the Rhine at 

 Bonn 188 Rheinland feet (193*6 English feet), and at Kbnigsvvinter 192 

 Rheinland feet (197-72 Enghsh feet) above the level of the sea. Barometer- 

 Hohen — Messungen des Rheinstroms, in Leonhard and Bronn's Neues Jahr- 

 huch jur Mineralogie, 5fc. 1835, p. 260. One Rheinland foot = 10298 En- 

 ghsh. 



II. Page 434. 



From the smallness of the scale to which my map has been reduced for 

 publication, it is scarcely possible to define the boundaries of the several mi- 

 neral formations with precision. Those who wish to examine the Sieben- 

 gebirge will do well to provide themselves with a copy of a geological map 

 published at Bonn in 1835 by Henry and Cohen. 



III. Page 442. 



M. Thomae, in the memoir cited in the next note, mentions the occurrence 

 of trachyte tuff in the lane leading from Nieder Bachem to Liessem, p. 43. 



IV. Page 447. 



A very detailed account of the Roderberg has been recently published, 

 entitled Der Vulkanische Roderberg bei Bonn. Geognostische Beschreibung 

 seines Kraters und seiner Umgebungen, von Carl Thomae. Bonn, 1835. 

 Those who wish to examine and understand the structure of this interesting 

 geological feature of the district should take this memoir as a guide. I ex- 

 tract the following particulars in this place, and I have refered to it in other 

 parts of this Appendix. 



The highest point of the crater is 330 Rheinland feet (339-8 English feet) 

 above the surface of the Rhine. He estimates the longest diameter of it at a 

 thousand paces, and the shortest at seven hundred paces. 



The lava at the north-east side of the crater was at one time quarried, in 



