704 PRINCIPLES OF STRATIGRAPHY 



of such cross-bedding is the tangency of the layers at the base, while 

 at the top erosion has sharply truncated them. 



This type of cross-bedding is not infrequently met with in 

 arenytes among the strata of all ages. The Medina sandstone 

 (Siluric) of western New York affords some excellent examples 

 of this type, and it is highly probable that the beds showing this 

 structure were originally wind-laid deposits. Other excellent 

 examples of such cross-bedding are shown in the Sylvania sand- 

 stone (Upper Siluric) of Ohio, Michigan and Canada (Figs. 

 119, 120) and in the White Cliff sandstones (Jurassic) of the Kanab 

 Plateau and in the La Platte sandstone (Jurassic) of Utah. Cal- 

 carenytes, too, sometimes show this structure, as noted above, for 

 the Junagarh limestone of India and for other modern deposits 

 recognized as wind-laid. The cross-bedding of the Somersetshire 

 oolite (Forest marble), referred to above (Fig. 121), appears also 

 to be indicative of the eolian origin of this rock. Excellent exam- 



FiG. 137. Eolian cross-bedding as found in desert sands. (After Walther.) 



pies of this type of bedding in a heavy-bedded, non-siliceous lime- 

 stone (calarenyte) have been observed by the author in the cut 

 througli the Warsaw (Mississippic) limestone on the Missouri Pa- 

 cific Railroad, south of St. Louis, Missouri. This is reproduced in 

 Figs. 122a and b, on page 577. Compare, also. Figs. 138, 139. 



Comparison of Types. A comparison of the three types of 

 cross-bedding, i. e., the delta, the torrential and the eolian, will show 

 the distinctive character of each, namely : uniformly sloping fore- 

 set beds in one series and generally on a large scale, for delta de- 

 posits ; uniform fore-set beds of small size and in successive but 

 similar series separated by horizontal deposits, for torrential de- 

 posits ; and oblique beds, variable in angle and slope within the same 

 and successive series commonly without horizontal dividing beds, 

 for eolian deposits. While these types grade into each other where 

 the deposits meet or overlap, it is not known that any one type of 

 cross-bedding is produced by another agent. Thus the torrential 

 type of cross-bedding cannot be readily conceived of as formed in 

 the sea, and the same may be said of the eolian type. The bedding 

 of a sand bar may perhaps show something analogous to the wind- 



