VA.LLBY DEIFT. 59 



valleys of Maine is tliat there is a profound difference between the sedi- 

 ments of the valleys above and below about 230 feet above sea level. 

 Below that level the country was beneath the sea, and is covered with 

 clays and other marine deposits. Unlike ordinary valley alluvium, the 

 marine beds do not as a whole show a level plain in the bottoms of the val- 

 leys. Over large areas the surfaces of the clay plains undulate somewhat 

 like the till beneath them, especially in the broad valleys which were arms 

 of the sea, several to 20 miles broad when the sea stood at its highest 

 level. As elsewhere noted, the cla5^s are thickest near the mouths of the 

 glacial rivers. Hence when we find marine deltas of glacial sediments in 

 rather narrow valleys, the offshore clays usually extend over the whole val- 

 ley and have a nearly horizontal surface across it. This closely simulates 

 fluviatile sediments. The present rivers began to flow at the time the sea 

 stood at its highest level. The fluviatile delta sands which these rivers at 

 that time poin-ed into the sea are easily recognizable and for a few miles 

 extend entirely across their valleys, like fluviatile drift. A little below 230 

 feet tiie sands no longer spread over the whole space then under water, but 

 form plains from 1 to 4 miles wide overlying the fossiliferous clays, and 

 follow not only the main valley but also sometimes lateral valleys which 

 were then straits, such as the line of sands that extends from the Andros- 

 coggin at Durham southward to Pownal. 



Above the level of 230 feet we find sheets of sediments covering the 

 bottoms of the valleys, usually terraced like the upper Connecticut Valley, 

 and in most cases extending from one side of the valley to the other. In 

 this portion of Maine (which was not in postglacial time beneath the sea) 

 we find the valley drift comparable to that of the rest of northern New 

 England. It will therefore be understood that the following remarks apply 

 only to that part of the State situated above about 230 feet. 



Over the tnove level regions the lowest layer of the valley drift is usu- 

 ally silt or clay, the upper layers consisting of coarser material, such as 

 sand or gravel. As we approach the highlands the sediments become 

 coarser in composition. Among the high hills the slopes are often 80 feet 

 or more per mile, and the valley drift contains cobbles, bowlderets, and 

 sometimes even bowlders. In general, the stones found in the valley sedi- 

 ments of Maine are very much less worn and rounded than those in the 

 kames and osars. Some exceptions ought to be noted. Thus, near the 



