1823.] the principal Mountain Chains of Europe. 147 



observes that it penetrates the coal measures in various manners; 

 sometimes it covers the coal immediately; more generally it 

 reposes on the sandstone, elevating itself above this rock in 

 domes, towers, and escarped rocks. When the transition rocks 

 are immediately covered by the red sandstone, it is difficult to 

 say whether the porphyry associated with the coal is referable 

 to the transition or sandstone series. The porphyry seldom 

 forms true beds in the coal measures, but rather transversal andin- 

 terposed masses. He adds, that these masses offer many analogies 

 with volcanic rocks, and inclines to favour the opinion, that the 

 pretended passage of the porphyry into the sandstone is an illu- 

 sion produced by regenerated porphyries ; i. e. by the subsequent 

 reunion of porphyritic debris. These remarks are applicable 

 generally to the porphyry associated in the coal districts of 

 Germany. From its intimate connexion in geographical posi- 

 tion with the coal districts, I have included it under the same 

 colour, though strongly inclined to consider it as of subsequent 

 formation. 



(L.) Coal and Porphyry of the Thv.ringerivalde.* 



The porphyry of the Thuringerwalde constitutes the highest 

 portion of that chain ; it contains, according to Keferstein, sub- 

 ordinate beds of coal between Ilmenau and Sahl. 



(M.) Coal, S)C. on the Western Borders of the Chains extending 

 from the Thuiingeruwlde. 



A small coal district occurs on the ..borders of the Saxon slate 

 mountains, not far from Steinach, near the point where they 

 join the Fichtelgebirge, and porphyry is found on the borders of 

 the Bohemerwald, near Ratisbon. 



(N.) Great Saxon District of Coal and Porphyry. 



This is an extensive district which may generally be described 

 as lying along the course of the Zwickau between Leipzig and 

 the Erzegebirge ; porphyry prevails. Coal accompanied by the 

 usual rocks occurs near Zwickau, at Schonfield, Planenschen 

 grund near Tharand, Sec. sometimes overlying, sometimes under- 

 lying, and sometimes associated with the porphyry .f This dis- 



* The following articles are chiefly from Keferstein. 



+ At Schonfeld, the coal alternates with porphyry, above which occur the following 

 beds : 1 . A conglomerate of porphyry and gneiss. 2. Bituminous shale with vegetable 

 impressions. 3. Red sand. At Zwickau the beds (beginning with the lowest), 1. VTacke. 

 S, Basalt. 3. Nine or ten coal beds alternating witli white grit and shale containing 

 vegetable impressions. 4. Sandstone. 5. Red grit. The coal field of Planeschen 

 grund is more extensive than either of the former ; here a range of sienite, extending on 

 the right bank of the Weisseritz, forms the fundamental rock on which a secondary por- 

 phyry reposes ; then succeed four beds of coal alternating with grit and shale, and 

 inclined at an angle of 65°. 



There is no bitumen in the coal of Schonfeld ; although it abounds at Planenschen 

 grund : the same fossil vegetation is presented in all these mines. (See Sternberg ' Flora 

 zur Vorvrelt.') 



i2 



