M. Reuss on the Magnetic Polarity of Basalt. 179 



they are perceptible as well as the hills themselves, are meri- 

 dional; and a quarter of a mile more south, is the pond of 

 Morbruch, a maar of some extent. Schulze." 



Addition to the foregoing Article : — On the Magnetic Polarity 

 of two Basaltic Rocks in the Lordship of Schrockenstein. By 

 M. Reuss of- Berlin, Counsellor of Mines.* 



To the very interesting discovery of magnetic polarity in 

 two rocks of basalt near Nurburg in the Eifel, published by 

 Mr. Schulze of Diiren, in the Jahrb. der Chem. u. Phis, (see 

 the preceding article in the Phil. Mag. and Annals) may be 

 added another made by myself in 1827, near the highWostrai, 

 in the lordship of Schrockenstein, in the Mittelgebirg. 



This high Wostrai forms in itself a small, rather insignifi- 

 cant cone, but which, owing to its high situation, overlooks 

 the whole neighbourhood, and affords an excellent prospect 

 of a great part of the Mittelgebirg on both sides of the Elbe. 

 Its elevation above the river near Aussig may be about 1800 

 feet. This cone is covered with wood to its summit, and is 

 precipitous on all sides ; only the top shows any rock unco- 

 vered, and forms a narrow coombe, falling from south to north. 

 In the steeper parts the basalt is separated into tabular masses ; 

 these tables, which are about six or eight inches thick, fall four 

 or five hours under nearly 24° W. On the west, the Wostrai 

 connects itself with the Skala, or rather forms the highest point 

 of it, and runs out in the southern and eastern gentle and well 

 cultivated declivity of the Gemeindeberg ; on the east the foot 

 of the cone falls in the equally well cultivated plain belonging 

 to the village of Malschen. 



The basalt is of a dark grayish black, very fne-grained in 

 the fracture, and contains very numerous but very small cry- 

 stals of pyroxene. There is no visible trace of magnetic iron- 

 stone, which is always distinguished by its metallic lustre. Its 

 polarity is remarkable, being so great that the needle at the 

 eastern foot of the basalt rock is moved 40°, and at the cone 

 itself 90° W. At the western foot of the rock the contrary 

 is the case; but this polarity is shown not only in the whole 

 mass of the rock, but likewise in the larger detached pieces, 

 and even in the smallest fragments, the north point of the 

 needle being at one end distinctly attracted, and at the oppo- 

 site end as distinctly repelled. 



The same polarity I discovered on the Breitenberg, which 

 rises to the south of the great Wostrai, about 1 0° to 15° higher, 

 is entirely covered with high forest trees, and presents only on 



* From Schweigger's Journal. 



2 A 2 the 



