i 



48 GEOLOGICAL MEMOIRS. 



and not in separate layers, yet so that while shells occur at the very 

 edge of the bank, fish are found by digging farther inland. 



The Crustacea however {Limnadice) are found at another portion of 

 the bank in Cjuestion (probably the site of an ancient pool). The 

 slaty clay has not yet been dug through, but extends uniformly down- 

 wards without any alteration. The upper layers are somewhat greasy, 

 perhaps from the remains of decomposed fish. 



About 40 wersts to the south of this locality commence the broad 

 endless plams of the Mongohan steppes. 



On the right bank of the Onon, about 30 wersts above the mouth 

 of the Turga, impressions of fish are also said to occm* ; according to 

 report, moreover, the slate is there fidl of little flakes of mica. 



[W. J. H.] 



On the Formation o/ Dolomite. By Prof. G. Forchhammer. 



[Oversigt over det Kougeliae Danske Videnskabernes Selskabs Forliandlinger, 

 p. 83-96, June 22, 1849.] 



Since Dolomieu first paid attention to the magnesiferous hmestone 

 of the Alps, called after him Dolomite, this rock has often been an 

 object of research; but only after L. Ton Buch had pointed out the 

 important part it plays in the Tyrol Alps and at several places in Ger- 

 many, has its influence on the geological history of the earth been 

 fully recognized. 



Carbonate of lime and carbonate of magnesia occm* in the earth 

 mixed in various proportions ; but nomenclature as yet has in nowise 

 determined to which combinations the terms ^'common limestone," 

 "dolomitic limestone," and '^ dolomite," should be respectively ap- 

 phed. 



\\Q have here to determine the proportions, in excess or other- 

 wise, in which the two isomorphous salts, carbonate of magnesia and 

 carbonate of lime, are combined. The other conditions, hardness and 

 specific gravity, are here of less im.portance, as they are independent 

 of the quantity of magnesia present. The structure of the stone, I 

 may remark, here as in the case of limestone, can be of httle im- 

 portance for the determination of the chfferent kinds. 



Our common hmestone contains a very small quantity of magnesia. 

 Chalk from Ahndelille, in the neighbourhood of Ringsted, is com- 

 posed of — 



Carbonate of lime 98-98G 



Carbonate of magnesia .... 0"371 



Sulphate of lime 0"073 



Phosphate of lime 0*045 



Silica 0-435 



Argilla and iron 0*089 



100-000 



It contains therefore about \ per cent, of carbonate of magnesia. 



