56 GLACIAL GRAVELS OF MAIXE. 



which overlies the till contains very few fossils, and over large areas i one 

 at all could be found. The lower beds often vary in composition. Gen- 

 erally they are a fine blue clay, but in many places they consist of a fine 

 sand, which is sometimes quicksand. These alternations of fine sand and 

 clay are in a great measure independent of the relief forms of the land, 

 and do not represent the horizontal gradations of sediment depending on 

 depths of water. They are rather such variations as could be expected in 

 a sea into which a great number of sediment-laden streams were pouring 

 and where the fineness of the sediments was determined chiefly by the 

 positions of the mouths of these streams. In the early part of this epoch 

 the streams were smaller than they were later, and were mostly glacial 

 streams. The positions of the mouths of the streams were constantly 

 changing during the retreat of the ice, and would be affected also b)^ 

 changes in the level of the sea. As elsewhere noted, what appears to be a 

 kame or osar border clay is sometimes richly fossiliferous. These fossils 

 were probably deposited in bays in the ice, into which the salt water 

 reached, and while most of the ice was still unmelted. They therefore 

 date from an early part of the marine-clay period in Maine. 



THE UPPER CLAYS : DELTAS DEPOSITED BY OEDINAEY RIVERS. 



In the upper layers of the marine clays and clay loams I have found 

 but few fossils. As noted elsewhere, the same observations have been made 

 by Professor Lee at Brunswick and Professor Stanley at Lewiston. The 

 probability of finding fossils in the upper claj^s is greatest near the sea and 

 away from the great river valleys. The clays are deepest in the larger 

 valleys and near where the great glacial rivers flowed into the sea. The 

 fact that fossils are rarest where the clay is deepest proves unfavorable con- 

 ditions for marine life near the mouths of both the glacial rivers and the 

 ordinar)'- rivers. In other words, the vast influx of ice-cold and muddy 

 fresh water during the final melting of the great glacier was destructive of 

 marine life. 



The rarity of fossils contained in the upper clays and silts makes it 

 very difficult to determine where the marine beds end and those of estuarine 

 and fresh water origin begin. For instance, a nearly continuous sheet of 

 clay extends from the sea up the valleys of the Kennebec and Sandy rivers 

 to a height of 450 feet or more. Below 230 feet this clay is usually dark 



