Explanation of Plates III. and IV. 



Plate III. Exposure of St. Peter sandstone northeast of Hesper, 

 and a half mile west of that shown in Plates I. and II. Looking north. 

 Selaginclla rupestris., U'oodsia ilvensis, Cystopteris bulbifera, and Rubus 

 bailey anus grow on the east side of this exposure. The sandy talus pro- 

 duces Polygonum tenue, P. douglasii, Potentilla tridentata, and the fol- 

 lowing trees and shrubs: Betula papyri/era (the most common), Quercus 

 borealis, Q. macrocarpa, Primus virginiana, and Amelanchier rotundi- 

 folia. (See pp. 225-7). 



Plate IV. Characteristic St. Peter standstone plants: 



Fig. 1. Polygon inn douglasii Greene. 

 Fig. 2. Aronia nigra (Willd. ) Britt. 

 Fig. 3. Polenlilla tridentata Sol. 

 Fig. 4. U'oodsia ilvensis (L. ) R. Br. 

 Fig. 5. Selaginella rupestris (I/.) Spring. 

 (See pp. 226-7). 



