270 Sir Alexander Crichton on some Parts of the Taunus ; 



to produce this appearance ; whereas, in its softer parts, the same may be 

 observed by letting fall a drop of acid on it. This rock, both in its slaty 

 form and also where it breaks into thicker and longer masses, abounds in 

 veins of compact carbonate of lime. It is used for architectural purposes. 



In the mountain of Schomburg this stone breaks into large thick blocks, 

 two of the sides of which are flat and nearly parallel : the others are splin- 

 tery. The slaty variety I met with in the valley of the river Aar, which falls 

 into the Lahn near Dietz. In this slaty kind it is common to find the carbo- 

 nate of lime in patches, giving an amygdaloidal character to the stone. The 

 true native situation of this rock is the dutchy of Dillenbourg. Here it is 

 always accompanied, as I am informed, with transition limestone, and contains 

 great beds of a very rich iron ore lying between the schalstein and limestone. 



At Dietz the transition limestone borders both sides of the river ; and im- 

 mediately reposing on this, at Oranienstein, is a thick hard bed of compact 

 crystalline dolomite. This is the newest formation which I saw in this neigh- 

 bourhood, excepting always alluvial deposits. 



The transition mountains which I have been describing are pierced in 

 numerous places by basalt. In the short distance between Ems and Holzapfel 

 are no less than four instances of the kind: — and one of these is accompanied 

 by circumstances deserving notice. Immediately behind the house of the 

 inspector of the mineral waters of Fachengen, a grauwacke mountain rises, 

 on the top of which is a basaltic quarry, of an imperfectly columnar structure. 

 Next to the basalt on one side is greenstone ; on the other side, mountain 

 limestone. The grauwacke lies at a high angle, and incloses the greenstone 

 and basalt, and the limestone has the appearance of dislocation. 



Of the Valley of the Mayne. 



The valley lying between the Taunus Mountains and the river Mayne con- 

 sists of shelly limestone and marie, which are easily examined in several 

 quarries on the declivities of the low hills which border the river. The spe- 

 cimens which I collected, were taken from a quarry near Oberrad ; from a 

 quarry at Mulbach, near to Wiesbaden ; and the rest from Hogheim, facing 

 Mayence. 



At Oberrad the beds are of various thickness, separated by beds of marie ; 

 this limestone in its lower beds is compact, fine-grained, and of a splin- 

 tery fracture. The uppermost bed is about three feet thick, and lies about 

 two feet under the surface. The next is about six feet thick : a much thicker 

 one follows. This limestone and the marie are full of shells, which according 



