178 Prof. J. Nbggerath on the Magnetic Polarity, tyc. 



does not seem to be confined to the rocks as far as they are 

 exposed, but probably descends deeper into the mountains, as 

 would seem from an uncovered part I noticed, lower down on 

 the south side. I marked the direction 

 of the slaty beds, and communicated 

 them to the Ober-ehifahrer, Mr. Bech- 

 er of Commern, who accompanied 

 me ; on his doing the same, we dis- 

 covered a difference. Our attention 

 being thus excited, I went round both 

 rocks, and holding the compass every- 

 where close to them, noted the direc- 

 tions of the needle, as represented in 

 the annexed figure*. The variations 

 of the needle were always sudden and 

 violent, so that its vibrations were few, 

 but rapid. The N.W. rock seems to contain a magnetic axis, 

 but not the other; in the meridian it attracts the northern 

 point of the needle, and on the cross line running through 

 the centre, the southern point turns towards the rock. 



" The colour of the mass is dark gray, in some parts iron 

 black, on the cross fracture conchoidal, without betraying to 

 the naked eye any foreign admixture, such as magnetic iron- 

 stone. It is probable that there are other points about the 

 surrounding basalt hills where the needle would be disturbed ; 

 but want of time, and unfavourable weather, prevented my 

 making further experiments. 



" From the Nurburg I went to the village of Kellberg, and 

 looked the following day for trachyte porphyry with crystals 

 ofalbite, about the cone called Freienhauschen. Here, be- 

 tween the hamlet of Kottelbach and the Hoch- Kellberg, are 

 two cones close together, to the N. the Brink, and to the S. the 

 Frauen, or Freienhauschen. On the first the mass of por- 

 phyry is of two kinds; the one apparently prevailing is of a 

 liver-colour with delicate admixed parts. This latter mass is 

 very distinctly formed in strata, and attached to, or more pro- 

 bably inserted in the other, dipping twelve hours, and dipping 

 pretty strongly to the E. Too much engaged in looking for 

 pieces of porphyry with remarkable crystals of albite, I suf- 

 fered the weak attractive power of the black trachyte to escape 

 my notice, on the spot, not perceiving it till afterwards in some 

 pieces I had taken with me. The strata in the Brink, where 



* It need perhaps scarcely be noticed, that the arrows in the figure 

 pointing towards the rock indicate a northern, and turned from the rock, 

 a southern attraction, and that the needle lying parallel to the rock is to 

 mark an indifferent position.— N. 



they 



