NOTES ON RIPPLE MARKS 125 



was mined for the Utica Cement Works, some ripples have been 

 disclosed that measure from 4 to 5 feet across from crest to crest. 

 This is in a somewhat thin-bedded dolomite, which contains some 

 sand. Evidently this limestone was not a shallow-water deposit. 

 The ripple-bedded layers lie some 100 feet below the base of the 

 St. Peter sandstone. 



The widest ripple marks that have come under my observation 

 are in a crinoid?! limestone in the lower part of the Burlington, 



Fig. 2. — Ripple marks on Jurassic sandstone, near Minnekahta, South Dakota. 

 One-half natural size. 



in the southeast part of Louisa County, in Iowa. These ripples 

 measure nearly 6 feet from crest to crest, and are at least 6 inches 

 deep. The presence of crinoidal remains in this rock, which con- 

 tains some shaly material, indicates, if not proves, deep-water 

 conditions. How deep? 



Higher up in the geological column I have seen some quite 

 large ripple marks in the Comanchean, in Texas, in a horizon near 

 the Kiamitia clay. About 17 miles west-southwest from Kerrville 

 such ripple marks occur in the bed of Guadalupe River (see Fig. 3). 

 They measure about 14 inches across and are about i| inches deep. 

 They are slightly unsymmetrical. The rock in this case is a mixture 

 of calcareous and shaly material, which contains variable quantities 

 of fine sand, so that some layers might more properly be called 



