10 Rev. W. D. Conybeare on a Geological Map of [Jan. 



is, according to Dr. Boue, much altered, and the limestone, 

 under the same circumstances, assumes a granular character. 

 Traces of coal occur on the borders of this chain in some places 

 on the E and S, and a conglomerate, probably belonging to the 

 newer red sandstone, often overlies and abuts upon the primitive 

 rocks in surrounding the chain. 



The intermediate Valley of the Rhine between these mountains 

 and the opposite group of the Black Forest, is principally occu- 

 pied by formations of the tertiary order. 



The Black Forest. — This range extends near the right bank of 

 the Rhine from Basle to Rastadt ; it rises gradually from the E, 

 and breaks down with a steep escarpment to the W. Granite 

 is the prevailing rock, occasionally associated with gneiss. A 

 porphyritic formation sometimes rests on the granite, and forms 

 summits. On the eastern slope, the range is covered by the 

 overlying red sandstone. The Odenwald rises in the prolonga- 

 tion of the same line between Heidelberg and Darmstadt ; its 

 constitution is exactly similar. The Spessart is a small insu- 

 lated granitic group, almost close to the NE end of the Oden- 

 wald. 



(G.) Chain of the Loiver Rhine, or Slate Mountains of the 

 Ardennes, Eiffek, and Rhingau. 



This is a district of low mountains exclusively occupied by 

 transition rocks (i. e. greywacke, greywacke slate, and transition 

 limestone), extending from the Meuse above its junction with 

 the Sambre, across the Rhine below Mayence to Marburg. This 

 chain is familiar to every continental traveller on account of the 

 magnificent defile which opens directly across it to give passage 

 to the rapid waters of the Rhine between Bingen and Bonn ; an 

 extensive and decided volcanic district partially overlies the tran- 

 sition rocks above Bonn. On the left bank of the river is a 

 region presenting plains covered with ashes, from which rise 

 some low but well defined craters ; on the right are the trachytic 

 and basaltic summits of the Siebenaeberire. This schistose 

 chain is skirted on the N by the formations of old red sandstone, 

 mountain limestone, and coal ; on the S also, the mountain lime- 

 stone occasionally appears ; but the new red sandstone generally 

 overlies the transition rocks immediately. 



(H.) The Haifa, 



This is the last of the insulated and protruding groups we shall 

 have occasion to notice. 



It exhibits granitic summits : but no gneiss or mica slate has 

 yet been found in situ. The granite is succeeded by clay slate, 

 and the usual transition series. The coal formation rests against 

 the transition series, and is followed by the new red. sandstone 



