A REPLACEMENT OF WOOD BY DOLOMITE 359 



specimen. The most noticeable feature in this part is the parallel 

 radial lines of buff dolomite. Adjoining lines usually are separated 

 by fine brownish black silica. 



Small dolomite crystals grouped radially about a center of 

 silica also can be seen in this part of the specimen. These groups 

 are made prominent in the hand specimen by the black silica cores. 

 They occur with apparent regularity throughout the dolomite, and 



Fig. 2. — Thin section showing compound dolomite crystals in siliceous matrix. 

 Replacement of dolomite by silica is illustrated around places marked "x." White 

 central part (at "x") is a hole in the slide where the dolomite has pitted out. The 

 fringe around the hole is silica, surrounded by the darker organic matter excluded by 

 the dolomite during growth. This same effect can be seen around most of the rhombs. 

 This section also shows second generation dolomite developing along the edges of the 

 older rhombs as at "v." Xgh- 



it was at first suggested by Professor Abrams that they might mark 

 the location of resin ducts. This seems doubtful unless the outer 

 part of the specimen is a petrifaction of bark. However, recog- 

 nition of wood structure throughout the dolomite is at best largely 

 a guess. 



Annual rings are not well preserved in the dolomite. In the 

 dark-gray siliceous part of the specimen, however, annual rings are 

 prominent. They are marked by the gradual darkening of color 

 from spring growth to winter. In one or two places there are 



