328 L. Hatch — Marine Terraoes in S.E. Connecticut. 



Conditions Necessary for the Carving of the Terraces. 



For the development of a series of terraces such as we find 

 in the Stonington quadrangle, it seems necessary to postulate a 

 number of advances and retreats of the sea. From a study of 

 the Coastal plain, Dr. Barrell has found that there has been a 

 rhythmic rise and fall of the land relative to sea level along the 

 Atlantic coast ever since the Cretaceous period, to account for 

 the unconformities between the marine beds.^ The advance 

 of the sea may have gone far on the crystalline rock, as pointed 

 out by Dr. Barrell, and may have done most of the work in 

 developing the flat upland areas found in the Appalachian and 

 New England regions. 



In the Stonington quadrangle the exact physiographic history 

 can not be worked out, but the following events seem to have 

 taken place : Formation of an erosional surface on a series of 

 complex igneous and metamorphic rocks, by subaerial and marine 

 agents. This was covered with enough detritus so that on eleva- 

 tion the rivers took courses to the sea independent of their former 

 valleys. This surface is now represented by the upland patches 

 at about 500-feet elevation. Incision of streams resulted, and 

 the region was eroded to submaturity before the next incursion 

 of the sea, which planed off most of the hill tops and divides 

 down to the present 400-foot level. This was followed by suc- 

 cessive rises and falls of the land in relation to the sea, which 

 produced the terraces at 300^, 200^ and 100^-levels. A possible 

 stand of the land at 40' lower than at present may be proved 

 in a region less covered by drift near the coast. 



On the whole, subaerial forces were probably more promi- 

 nent in carving the region into its present form than marine, 

 although wave erosion was probably the agent which planed 

 down the divides and reduced the hills to common levels. 



While wave planation was going on along the shore, sub- 

 aerial forces were doing much to remove the higher land in 

 the interior. Thus the extensive lower surfaces along the 

 Quinebang and upper Thames rivers (Moosup quadrangle) were 

 probably developed while the waves were attacking the very 

 resistant rocks farther south. The difference in the amount of 

 flat upland north and south of the group of high hills in North 

 Stonington and Voluntown Townships is significant of the 

 difference in the two erosional processes. 



Indistinct benches (50-60 feet above the terrace levels) can 

 be seen in the profile of many of the river valleys to the north 

 and in the upper levels of the smaller hills. These probably 

 show the temporary base levels established in the river valleys 



*Bull. Geol. Soc. Am., vol. xxiv, p. 688, 1913 ; this Journal, vol. xl, p. 9, 

 1915. 



