Handbook of Paleontology 



45 



the deepest waters are deposited in the previous zone' of 

 mud deposition. If subsidence goes on, the sea extends 

 farther inland and the progressive succession of fine de- 

 posits upon coarser continues. This relation of the dif- 

 ferent beds is known as progressive overlap (figure 4) 

 and this particular type as marine transgressive overlap 

 (Latin transgressus, a passing over or across). If the 



Figure 4 A Marine transgressive overlap : finer beds deposited 

 upon coarser. B Marine regressive overlap : coarser beds 

 deposited upon finer. 



land is rising instead of sinking the process is reversed, 

 the sea retreats from the land, shallow waters take the 

 place of deeper waters and coarser sediments are de- 

 posited upon finer materials. Tfys is known as marine 

 regressive overlap (Latin regressus, a going back or re- 

 turn). Overlap may be marine or nonmarine. In marine 

 deposits progressive overlap is toward the source of sup- 



