August, 1841.] 75 



and may therefore have a power of assuming definite forms. The 

 oxide of iron in the ashes is commonly derived from the decompo- 

 sition of pyrites, while the lime and magnesia in the coal are pro- 

 bably in the state of carbonates, unless where the production of 

 sulphuric acid by the decomposition of the pyrites has converted 

 the former into gypsum and the latter into epsom salt. From 

 this latter play of affinities the carbonate of iron would be produ- 

 ced, and subsequently the sesquioxide, often seen covering the in- 

 terstices of outcrop coal and forming bog ore in the springs which 

 proceed from coal seams, the coal in the meantime retaining the 

 form impressed by the agency of the silicate of alumina, and hav- 

 ing a portion of its interstices or those of the underlying slates 

 filled up with crystallized sulphate of lime. 



Admitting the justness of this view of the causes which produ- 

 ced crystalloid forms in coal, we have no more difficulty in ac- 

 counting for the number of different forms which it occasionally 

 exhibits than for the analogous variety in regard to other minerals ; 

 the carbonate of lime, for example, which, as is well known to 

 mineralogists, takes on a far greater number of distinct forms. 



Prof. Bailey stated, that he had recently examined specimens 

 of Calcareous marl from the cretaceous formation discovered by 

 J. N. Nicollet, Esq., on the Upper Missouri, above the mouth of 

 the Sioux river. These specimens proved to contain fossil Fora- 

 minifera, (Polythalamia of Ehrenberg,) similar to those previ- 

 ously detected by Prof. Bailey in the calcareous portions of the 

 same formation in New Jersey and Alabama. 



He also mentioned certain silicified wood found near Fredericks- 

 burg, Va., in the feldsphalhic sandstone, called by Prof. W. B. 

 Rogers " upper secondary sandstone." This wood is in a pecu- 

 liar state of preservation, the vegetable matter having been com- 

 pletely replaced by silica, without any filling up of the cells or 

 tubes. In consequence of this state of the wood, it is easy to 

 subject it to microscopic examination without the trouble and ex- 

 pense of forming polished slices. All that is required is to break 

 off thin pieces with the point of a knife and moisten them ; they 

 then show the most delicate markings of the tissue beautifully 

 preserved. The discs with concentric rings, and other characters 

 peculiar to Conifera, are so distinctly visible as to leave no doubt, 

 that this wood which is commonly called in Fredericksburg, 

 " Petrified hickory," is really fossil pine. In the same formation, 

 fossil plants of the family Cycadeas, have been detected. 



