128 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 3, 



traversed at right angles to the strike and almost vertical cleavage- 

 planes by a powerful dyke of basalt, which is exposed near the town. 

 Another dyke is seen in the Ahne Thai on the Habichts Wald, from 

 which lateral injections of tabular horizontal beds of basalt have been 

 forced into the Muschelkalk. 



Over the Muschelkalk occur in ascending order: — 1. Alternating 

 beds of sand and clay, sometimes the one and sometimes the other, 

 resting immediately on the secondary rocks. In one of these lower 

 beds of sand are thin bands of sandstone, containing numerous vege- 

 table impressions, amongst which those of Taxus and Cypressus have 

 been made out. 



2. A bed of clay, four or five feet thick, forming an underclay to 

 the Brown-coal : this clay (blauer Letten) is generally of a dark 

 bluish colour. 



3. Brown Coal : these beds are here from 3Q to 40 feet thick, 

 and are extensively worked to supply the neighbourhood with fuel. 

 In some places the Coal-beds crop out on the surface, and the coal is 

 worked in open cuttings. In general character it is compact and 

 earthy, of a uniform texture, and without any trace of vegetable 

 organisms. Occasionally it acquires a brighter lustre, and is more 

 easily broken, and is then called Glance-coal. This generally occurs 

 in the neighbourhood of the basalt. 



4. A bed of clay, about 4 feet in thickness ; generally similar to 

 that below the Brown-coal. 



5. Marly yellowish sand, containing marine shells. The only 

 section of this bed which I saw^ w as in the Ahne Thai, where it occurs 

 in a deep ravine ; here the beds have been much disturbed by the 

 protrusion of the igneous rocks. It is not well exhibited. The 

 fchalls are chiefly small, and much broken. A list of them has been 

 published by Dr. Philippi of Cassel in 1844*, from which it appears 

 that at least 24 species are identical with those of the Mayence basin. 

 There is no list of synonyms supplied by Philippi ; such a list would 

 probably give a greater number of identical species in the two for- 

 mations. 



6. Loose incoherent sand, locally called Trieb- or drift-sand, from 

 its tendency to drift into the shafts, and other works of the coal-pits. 

 It constitutes the greatest difficulty of the workmen in driving their 

 adits and galleries, and has occasioned the abandonment of more 

 than one working. Large blocks of quartzose sandstone occasionally 

 occur in this sand, some of which are said to contain marine shells, 

 others are full of casts of the stems of plants. 



These beds have all a slight inclination, varying more or less in 

 different places, towards the centre of the basaltic hill which con- 

 stitutes the summit of the Habichts Wald. (See fig. 1.) The Brown- 

 coal dips under the basaltic mass which forms the plateau of the top 

 of the hill. This phsenomenon of the Brown-coals dipping under 

 the basalt, which I have observed in other places, will be alluded to 

 again hereafter. 



* Philippi, Beitrage, &c. 



