36 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
Lepidomelane, Scottish. 
Oxygen. 
Silica, : P : ; a pO 28 21°46 2L°46 . . eae 
Atamine, ts ge ee 5-71 ACh "ip 
Ferric Oxide, : ; : ~ ae 4:2 
Ferrous Oxide, . : ' et Oo °63 
Manganous Oxide, : : kes) “42 
Lime, ; : : : . eos 6 
Magnesia, .( 5. 38 Apes pees eee roe 
Potash, : : a eae 2 
Soda, : f : : Pele G7, DAL 
Water, : ; : A oe 3°49 
Lepidomelane, Irish, 
Oxygen. 
Silica, é f s : 5 S062 LOwad | OCD Sm: Palme 
Alumina, . 3 ‘ 5 liane) 8°15 
Ferric Oxide, : : : . 24:09 12 ee 
Ferrous Oxide, 2: '70 6 
Manganous Oxide, : yp. exer 3 
Lime, . ‘ ‘ , ‘ . ase “4 
Magnesia, : , 4°81 92 a aR | 
Potash, : , e : a One 1:48 
Soda, . ; ‘ ; : ‘ Dealt -08 
Water, DSi yaa 
These ratios show, firstly, that, as is usual in the micas, the oxygen ratio of 
the bases is, in each of the above, in excess of that of the silica. 
Secondly, that the ratios of the sesquioxides to the protoxides in Biotite 
and Irish lepidomelane are inverted ; being in Biotite only half of that of the 
protoxides, while in the Irish lepidomelane it is twice as great as that of the 
protoxides. 
The foreign and Scottish Haughtonite is evidently the same compound ; 
and this is one which stands intermediate between Biotite and Irish lepidome- 
lane ; the oxygen of the protoxides and sesquioxides being in,Haughtonite more 
nearly equal in amount than in either of the other species. 
And what I have called the Scottish lepidomelane is, as regards the 
balancing of the oxygen of the bases, more closely associated with Haughtonite 
than it is with the Irish lepidomelane. 
That which really, however, constitutes the distinguishing features of these 
micas is the state of oxidation or the iron. 
In Biotite the relative proportion of ferrous to ferric oxide is as 25 to 1; 
in Scottish Haughtonite as 4 to 1; while in lepidomelane these proportions are 
