LEWISTON-DUEHAM SEEIES. 203 



rivers were pouring a vast body of muddy water into the sea, and extensive 

 deltas of sand and clay were being formed off the coast of that period. 

 Above the sea A'^ast rivers occupied the valleys. They were laden with 

 sediment, and rapidly filled up their valleys with alluvium or valley drift. 

 At first the sediment was clay, but later the floods were higher, or the 

 slopes steeper, and sand was deposited by the swifter waters. This sand, 

 being poured into the sea by the Androscoggin and other rivers, was car- 

 ried far and near by the tidal currents and spread over the previously 

 deposited marine clays. A broad area of delta sands brought down by the 

 Androscoggin at this time extends from Lewiston to Brunswick and Tops- 

 ham, and almost to Bath; also from Durham southward to Yarmouth. 

 The area of this delta sand is diversified by frequent dunes of blown sand. 

 A small portion of tlie sand overlying the marine clays may be due to 

 erosion of the till by the sea. But this sand is not most abiuidant next the 

 high hills, and there is no body of beach gravel corres]Donding to the sand. 

 It is plainly delta sand bi'ought down by the Androscoggin, which not only 

 emptied into the sea near Lewiston, but also near the south end of Sabatis 

 Pond by way of Leeds. 



The Lewiston series of discontinuous domes and mounds ends near 

 the west line of Durham. About 3 miles southwest of this point another 

 series of mounds and broad plain-like ridges begins and extends past West 

 Durham into the northern part of Pownal, where the series ends, unless a 

 small ridge near Pownal Center be a connection of the series. Here, in 

 Lewiston, Durham, and Pownal, are illustrated the difficulties of classifying 

 glacial gravels. According to general analogy, the gravel systems end 

 in either a delta-plain or they become discontinuous and form a series of 

 short ridges and domes, which become smaller and smaller toward the 

 south, and the intervals between them longer and longer. The Lewiston 

 series ends in the manner last mentioned near the Androscoggin, in the 

 northwestern part of Durham, and the West Durham series ends in the 

 same way in Pownal. These series are situated nearly in the same straight 

 line, and the interval between them is less than 3 miles — facts which favor 

 the theory that they are a continuation of the same system and were depos- 

 ited by the same glacial river. But each series ends in a way characteristic 

 of the terminations of the independent systems, and I therefore hesitate to 



