EXPLANATION OF PLATES 661 



Plate 47. — Types of Sand Geains 



FiGUEE 1. — Saint Peter Sand Granules, Ordovician Age; Saint Paul, Minne- 

 sota. (X 201/2.) 



Well assorted, pure quartz ; seolian type, probably derived from 

 water-shaped granules. Supplied by Prof. C. P. Berkey. Re- 

 fleeted light. 



FiGUEE 2. — Same as Figure 1, l)ut of average coarser Texture; Minneapolis, 

 Minnesota. (X20%.) 



More of the subangular variety of granules shown, and some 

 indicating secondary enlargement. Supplied by Prof. C. P. Ber- 

 key. Reflected light. 



FiGUEE 3. — Sylvania Sand Granules, Silurian Age; Pit {near Top) National 

 SUica Company, Monroe County, Michigan. (X 20i/^.) 



Well assorted and rounded, pure quartz ; seolian type. The finer 

 specks between the granules represent small rhombohedrons of 

 dolomite secondarily introduced. Perfect rounding in granules 

 1/10 millimeter and less in diameter. Collected by the author. 

 Reflected light. The Saint Peter is regarded as the most probable 

 source of the Sylvania. 



FiGUEE 4. — Sylvania Sand, coarser average Texture than Figure 3, Detroit 

 Salt Shaft, near Top. (X 201/2.) 



Finer specks of dolomite between granules, and not original. 

 Collected by the author. Reflected light. 



FiGUEE 5. — Sylvania Granules, from small concretionary-like Pellets, disin- 

 tegrated J)y use of Acid; Pit National Silica Company, Monroe 

 County, Michigan. (X20i/^.) 



In such pellets the assorting of the granules is least perfect. 

 Collected by the author. Reflected light. 



FiGUEE 6. — Sylvania Granules, from Pit of the American Silica Company, 

 Rockwood, Michigan (4 Feet from Top). (X 20i^.) 



This assorting was entirely natural, and, combined with the 

 remarkable rounding, is the most perfect specimen of seolian sand 



XLVI — Bull. Geol. Soc. Am., Vol. 21, 1909 



