44 Nezv York State Museum 



sion. Fossils are flattened out and in the case of pebbles 

 the thin layers or laminae are bent about the inclusions. 



Cross-bedding or false bedding is another type of origi- 

 nal structure found in stratified rocks and is seen to best 

 advantage in delta deposits (figure 3). In this structure 

 certain laminae of the deposits lie in a position which is 

 oblique to the main stratification. A delta which has been 

 formed through deposition in standing water shows three 

 types of beds in its structure — bottomsets, topsets and 

 foresets. Bottomsets are formed of the finer materials 

 that wash out and settle on the floor of the body of water 

 in which the sediments are being deposited. They are 

 nearly horizontal in position. The topsets are formed of 

 the material washed over the upper surface of the delta 

 deposit. These layers have a primary dip which is the 

 same as the slope of the subaerial surface of the delta. 

 The foresets are composed of the materials carried over 

 the front of the delta into the water. They are oblique 

 to both the topsets and bottomsets and their primary 

 angle of dip is the angle of repose of materials under 

 water, that is, the angle at which the sediments can come 

 to rest and hold their position. Cross-bedding may also 

 be found in sand bars in rivers, in sand reefs, in current 

 deposits in the sea, in torrential deposits and in eolian or 

 wind deposits such as sand dunes. 



As has been pointed out above, in marine deposits the 

 coarser deposits are near the shore and the material grows 

 finer and finer as one approaches deep water. If the land 

 is sinking the sea encroaches upon it, depositing the coarse 

 beach sediments upon what was previously a land erosion 

 surface. Deep waters replace shallow waters. The fine 

 muds of the deep waters are laid down upon the sands 

 of previous shallow waters and limy muds or oozes of 



