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NEW YOPvK STATE MUSEUM 



change. The thin portion does not represent the whole of the 

 thicker portion but only the upper part. It likewise shows how 

 within a short distance new members may appear below the one 

 forming the base in the first section. 



With the normal conditions thus outlined we are still con- 

 fronted by another fact which seems to form a marked exception 



Fiff. 6 



to the general rule. We not infrequently' find clastic limestones 

 whose character, resting directly on an old land of silicious rocks 

 on which they were deposited, indicattes a shallow sea. Never- 

 theless silicious clastic material is almost or quite absent from 

 these rocks. In such cases the only explanation seems to be that 

 the water was shallow a considerable distance from shore and 

 that the shore was worn down so low that little or no detritus 

 could be supplied ; i. e. worn down to a peneplain. 



