12 



The Scottish Naturalist. 



carboniferous rocks. Its presence there had been known long 

 before it was re-discovered, some 25 years ago, through its outcrop- 

 ping at different points ; as the warpers of a by-gone generation 

 used to collect pieces of the earthy portion of it. known to them 

 as " keel," wherewith to mark the length on their webs. The bed 

 of limestone, in which this Haematite lay, is one of a series of 

 compact or crystallized limestone, of more or less purity, but not 

 of great extent. This bed rests upon a bed of shale, containing 

 numerous fossil remains of corals and small shells. Above it lies 

 a thin bed of " Productus limestone," so called from the number 

 of shells of Productus embedded in it. 



The bed in which the Haematite was lodged, in a pocket or 

 lode, deserves a little notice. From a compact or crystalline 

 limestone, i.e., carbonate of calcium, or lime, it passes at the top 

 into dolomite, which is a carbonate of magnesium and calcium, 

 in nearly equal proportions. When limestone passes into dolo- 

 mite, the limestone or carbonate of calcium loses bulk, as may be 

 seen in this specimen, hence the drusy cavities in it. The condi- 

 tions necessary for this change are, the presence, say in spring 

 water, of the bi-carbonate of magnesia, one of the common con- 

 stituents of spring water. When this permeates or passes over 

 limestone or carbonate of lime, the presence of carbonic acid gas 

 in the water causes the lime to pass into a bi-carbonate. The 

 bi-carbonate of magnesia (consisting of carbonic acid gas and the 

 carbonate of magnesia), would attack the carbonate of lime and 

 the neutral carbonate of magnesia, (uniting therewith dolomite, 

 composed of both lime and magnesia), would remain, the water 

 that brought the carbonate of magnesia removing the carbonate of 

 lime. (Bischof, vol. 3, 166. 174.) This becomes purer; and we 

 have the crystallized Dolomite, or Rhomb, or Bitter Spar. The 

 specimen shows some calespar still remaining, the pseudomorphs 

 not having covered these. 



The pocket or lode in which this Haematite lay is extremely 

 interesting. It occurs where there is a rent or fissure running 

 right across the bed, and does not at all form an even bed or 

 cavity, the limestone there being more like pudding stone. 



The Haematite has the appearance, so to speak, of having been 

 " run in," adapting itself to the spaces at its disposal, by imbed- 

 ding itself round and upon the nodular surface, occupying even- 

 available space 



