20 GEOLOGICAL MEMOIRS. 



to the surface in highly inchned strata, contains the carbonate of mag- 

 nesia, not mixed with the carbonate of Hme, but in the condition of a 

 true dolomite. The change of the muschelkalk into dolomite is 

 always the more complete the nearer the limestone approaches to the 

 fissure through which the anhydrite has been elevated. The higher 

 strata contain only a small proportion of dolomite, which has not 

 essentially altered their character, which in the vicinity of the fissure 

 was entirely destroyed. 



The peculiar nature of the matter filling the fissures in the masses 

 of gypsum at Segeberg and Liibtheen leads to the conclusion that 

 the anhydrite on its elevation must also have broken through beds 

 of limestone, and partially changed them into dolomite, although 

 these strata have not been forced up to the surface, as has actually 

 occurred at Limeburg. From the disposition of the beds, and from 

 the nature of the matter in these fissures, it further appears that the 

 mass of gypsum now exposed must have reached the surface after 

 the tertiary formations were deposited. On the other hand, the me- 

 chanical disturbances which the beds of the inferior rocks have under- 

 gone, and the chemical alterations of the limestone strata which come 

 more immediately into contact with the fissure of elevation, probably 

 belong to a very much earlier period than that of the elevation of 

 the anhydrite, which, as the nature of the matter filling the fissures 

 shows, has taken place slowly and probably with interruptions. 



[J. N.] 



Mud of the Nile, 



The following analysis of the mud of the Nile, by M. Lassaigne 

 (Journ. de Pharm. t. v. p. 468), is more recent and complete than 

 that given by Lieut. Newbold from Regnault, in the last number of 

 the Quarterly Journal of the Society * . 



Silica 42-50 



Alumina 24*25 



Magnesia 1 '05 



Peroxide of iron 13' 65 



Carbonate of lime 3*85 



Carbonate of magnesia 1*20 



Humic acid 2*80 



Water 1070 



100-00 



Vol. iv. p. 341. 



[J. N.] 



