228 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.53. 



The most interesting features of these calcites are their inclusions 

 and exclusions of wood fiber. The relations of these can be best 

 appreciated by reference to the illustrations accompanying this 

 article. Their main features may be summed up here. Toward the 

 center of each grain a portion of the wood fiber is preserved as an 

 inclusion. The cells have not been greatly distorted, but the out- 

 lines of the groups of cells are determined by the crystallographic 

 character of the grains. As a result of the elongation of inclusions 

 in poij^synthetic twinning lamellae curious symmetrical figures have 

 been produced, some of them resembling insects. The cells are com- 

 pletely enveloped in calcite substance, and no silica has been observed 

 in any of the included portions of wood. 



Surrounding the central group of wood cells there is usually a zone 

 of entirely clear calcite, although in some instances the cells extend 

 outward and are continuous with those outside the crystal. Toward 

 the outer edge of the clear zone there is usually a band of very 

 minute, disrupted fragments of cells; and these often descend along 

 the boundaries of twinning lamellae into the mass of undisturbed 

 cells at the center. 



The margins of the crystals are generally sharply outlined against 

 the darker wood, and the crystal faces are always distinctly curved. 

 The phenomena exhibited outside the crystals are also noteworthy. 

 In all cases where any considerable proportion of a calcite crystal 

 is clear a dense black rim surrounds it. This is evidently composed 

 of wood cell material crowded out of the growing crystal. The wood 

 structure just beyond this rim is sometimes curved around the crys- 

 tals, although usually no effect whatever can be observed. These 

 relations show that the wood must have been decomposed to such 

 an extent that it soaked up the solutions as does a sponge, and had 

 lost practically all rigidity, so that compression exerted by growing 

 crystals produced no effect beyond the cells in the immediate neigh- 

 borhood of the crystals. 



Outside of the calcite crystals the wood cells are, in general, very 

 well preserved as dark-brown carbonaceous matter. Between crossed 

 nicols all openings are seen to be completely filled with quartz, an 

 individual crystal occupying each cell. The deposition of this has 

 evidently taken place from solutions which permeated the whole 

 cell structure; and since crystallization occurred about as rapidly on 

 one side of a cell wall as on the other, the structure was not dis- 

 torted thereby. 



A certain amount of distortion is shown by the wood cells, but it 

 is of such a type as to indicate that it was produced b}'^ the pressure 

 of overlying sediment on the rotted wood, rather than by the growing 

 of crystals. If anything the cells included in the calcite grains are 



