MARYLAND GEOLOGICAL SURVEY 135 



a simple uplift and pause, the terrace outside would have been formed, 

 but the valleys would have been cut to the level of the terrace, and rivers 

 swinging in these drainage ways would have widened them, opening up 

 a flood plain. Examination shows, however, that these valleys were 

 deeper before the terrace outside was formed and then filled with many 

 feet of sediments which are continuous with the depositing of the terrace 

 along the border of the formation. It is, therefore, clear that the land 

 must have stood at a higher elevation when these valleys were cut and 

 must have been depressed and the drainage ways drowned, like the pres- 

 ent estuaries of Chesapeake Bay, in order to receive these sediments. 



Second. The deep valleys of the principal rivers, taken in connection 

 with the gentle sloping of each terrace towards their axes and the small 

 thickness which each one of the surficial formations has developed in 

 these basins shows that the principal valleys in the Coastal Plain could 

 not have been cut to their present depth during the post-Lafayette uplift 

 alone. Otherwise the Sunderland formation would have either devel- 

 oped a much greater thickness in these drainage ways or else have sloped 

 toward their axes at a very much greater angle. It is then evident that 

 the post-Lafayette erosion only partially excavated the valleys now occu- 

 pied by the more prominent streams of the region, and that they have 

 been deepened during successive uplifts. What is true of the Lafayette- 

 Sunderland relations is also true of all the others. Neither the Wicomico 

 nor the Talbot terraces have developed any great thickness in these main 

 drainage ways and each one slopes gently toward the estuaries. 



Third. Each one of the terrace formations has re-worked and re- 

 deposited over extensive areas great portions of the underlying Tertiary 

 and Cretaceous deposits, and wherever this occurs, they are found to lie 

 directly on the eroded surfaces of these beds. This show's that the older 

 formations were at no time covered with a thick deposit of sand and 

 gravel, and that the seas which deposited these various terrace forma- 

 tions advanced over a region already stripped in large measure of the 

 deposit laid down by the preceding incursion. Had there been but one 

 period of uplift and erosion during post-Lafayette time, the Sunderland 

 formation would have covered the surrounding country with a thick 

 mantle of debris and the succeeding formations would have been depos- 



