80 PHYSICAL GEuLOGY 



Grabau, A. W., — Principles of Stratigraphy, pp. 467-475; 718-721. 



Gratacap,. L. P., — Opinions upon Clay Stones and Concretion : Am. Naturalist, 



Vol. 18, 1884, pp. 882-892. 

 Merrill, G. P., — Rocks, Rock-Weathering, and Soils, pp. 35-37. 

 Nichols, H. W., — New Forms of Concretions: Field Columbian Museum, Geol. 



Series, Vol. 3, No. 3, 1906, pp. 25-54. 

 Sheldon, J. M. C, — Concretions from the Clay Stones of the Connecticut Valley. 



General 



Hobbs, W. H., — Earth Features and their Meaning, pp. 180-194. 

 Ries and Watson, — Engineering Geology, pp. 295-357. 



Topographic Map Sheets, U. S. Geological Survey, Illustrating the Work 



of Ground Water 



Arredondo, Florida. Greenville, Tennessee-North Carolina. 



Bristol, Virginia-Tennessee. Williston, Florida. 



Weingarten, Missouri-Illinois. Standingstone, Tennessee. 



Princeton, Kentucky. Lockport, Kentucky. 



Kingston, Tennessee. Waterloo, Illinois. 



