22 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.38. 



Upon the types described arc frequently subsidiary growths, giving 

 rise to strange and ungainly forms. An example is shown in fig. 13, 

 where a slimier pile of small tablets has grown out at an angle from 

 the main mass. There is evidently little regularity in the manner of 

 attachment of these secondary members. 



Symmetrical rosettes of the nature shown in fig. 5 are rare. Their 

 regularity of structure is interesting. They are built up from a cen- 

 tral plate by the piling around of other and smaller plates, with ever 

 increasing inclinations to the central one, until the uppermost is 

 nearly on edge. During their growth the e-axis of the consecutive 

 individuals departs more and more from a vertical position, and the 

 b-axis, so to speak, makes many complete revolutions in its several 

 positions. 



Fig. 12 represents the rare occurrence of two aggregates slightly 

 intergrown. There are only two other cases of attachment in the 

 entire suite. 



An unusual radiate assemblage 1 , composed of numerous elongated 

 plates diverging from a center, is shown in fig. 14. This well illustrates 

 the existence of two molecular forces of a somewhat different order, 

 the one developing thin tables and the other uniting these in a com- 

 mon point . 



Finally, fig. 15 pictures a development represented only twice in 

 the present collection and resembling some of the barites fromVilbel, 

 Germany, as described by Delkeskamp. a This example consists of 

 a thin, irregular sheet, with a surface of numerous globular masses, 

 2 to f) mm. in diameter. It is entirely concretionary in nature (as 

 the microscope also shows) and would seem to represent a case in 

 which the crystallizing force was insufficient to inhibit a complete 

 concretionary development. 



Microscopic. — Several thin slices of the specimens were studied 

 under the microscope. Three cases were considered: 



]. Sections cut parallel to the basal plane, c. These show numer- 

 ous rounded and some angular quartz grains, set in a cement of 

 barite. The grains are usually from 0.25 to 0.5 mm. in diameter, and 

 are rarely in contact with one another. The barite has the same 

 orientation throughout, extinguishing simultaneously. It possesses 

 t wo good cleavages parallel to the m (1 1 1 ) faces and crossing at angles 

 of 78° and 102°; the more perfect basal cleavage is in the plane of 

 the slide, and consequently not visible. A small amount of yellow, 

 opaque, pulverulent limonite is present, either staining slightly the 

 cleavage cracks of the barite and the edges of the quartz grains or 

 forming small aggregates. No other constituents could be deter- 

 mined. The material is remarkably clean and pure. 



"Xcils.hr. Naturw, Halle, vol. 75, 1902. 



