REVIEWS 647 



Some of the author's detailed conclusions are as follows: 



1. The composition and texture of a sandstone may furnish criteria regard- 

 ing its derivation and transportation, but not regarding its method of depo- 

 sition. 



2. The history of the sand grains of a sandstone is usually so complex 

 including transportation successively by winds, streams, and waves, that 

 textural criteria afford no proof whatever of the nature of transportation, even 

 to the last deposit in which the sand is found 



3. The structural and stratigraphic relationships in the field, including 

 such features as the character of bedding, cross-bedding, unconformities, lateral 

 gradation and similar associated phenomena, constitute the only valid criteria 

 for determining the conditions under which a deposit was last laid down, 

 and these may sometimes give a clue to the method of transportation to that 

 particular resting place. 



4. The purity of the St. Peter sandstone, while very remarkable, as com- 

 pared with that of average sandstones, is ... . not sufficiently different from 

 that of associated marine sandstones to demand any essentially different 

 explanation of origin; .... 



5. Size of train, in pure quartz sands, in general, is limited by the size of 

 quartz grains in average igneous rocks, and is not a satisfactory criterion of 

 wind-blown sands. 



6. The size and uniformity of grain in the St. Peter is so near that of the 

 Roubidoux marine sand, that no discriminations as to origin can be made on 

 such a basis. 



7. The degree of rounding and frosting of grains, which has been used as 

 one of the chief argmnents for eoHan origin of the St. Peter, may often be 

 masked by secondary quartz enlargement, but making due allowance for such 

 modification, the St. Peter cannot be distinguished, on this basis, from the 

 marine Roubidonx, or from older Cambrian sandstones 



8. The St. Peter shows bedding better developed than cross-bedding, and 

 does not show typically developed d\uie-structiu"e, even in the protected basal 

 layers in the valleys of the old erosion surface 



11. Limestone layers occur at many horizons, particularly at the south, 

 but are known as far north as north central Iowa and northern Illinois, and 

 indicate marine deposition. 



12. Oscillation ripple-marks in sand layers, marine fossils in limestone beds 

 . . . .occur in Arkansas and ^Missouri, next above the unconformity [at the 

 base of the series], showing submergence before the advance of the sand into 

 the region. 



13. Marine fossils are foimd in the St. Peter as far north as Mmneapohs, 

 not only in the uppermost transition layers, but also at three horizons, more than 

 60 feet below the top. These would not appear to have resulted from working 

 over of dune deposits. 



