WAS THERE AN INTBRGLACIAL PERIOD IN MAINE! 285 



around the end of the wooden part of the dam and eroded a channel in the 

 earth, thus aifording a fresh section down to the solid rock. At the bottom 

 were several feet of a hard, tough, clayey till that resisted erosion wonder- 

 fully and broke up into blocks 2 to 3 feet in diameter. 



Above this was a lighter-colored and less compact till forming a north- 

 and-south ridge or elongated drumlin. The material was indistinctly 

 arranged in layers, yet was not an osar composed of water-transported 

 matter, but was true unmodified till. The great contrast between the tough 

 under stratum and the more siliceous overlying layer made me suspect that 

 here were the ground moraines of two different ice-sheets. Subsequent 

 observations in many parts of the State have convinced me that this phe- 

 nomenon, which is a very common one, is probably due to the overlap of 

 till derived from two different kinds of rock. Thus at South Twin Lake 

 the local rocks are slates and other fine-grained schists. The lowest (blue) 

 stratum of the till is derived from the local rocks, while the (iverlying ridge 

 (also a part of the ground moraine) is composed of matter transported from 

 the granitic region about Mount Katahdin, situated not far to the north. 

 This overlapping of till having differeiit characters is found wherever the 

 ice passed from one kind of rock into an area of another kind. We do 

 not need to postulate two glacial periods in order to account for it, although 

 that is certainly possible. It is just what should be expected in the case of 

 an ice-sheet moving over areas of different kinds of rock, provided the 

 ground moraine was not all formed simultaneously, but each region was first 

 an area of denudation and subsequently of accumulation. During the 

 first pei'iod of denudation the scratching was produced. The first of the 

 embayed ground moi'aine would be composed chiefly of local mattei', which 

 would subsequently be overlain with far-traveled matter. 



All parts of the State have been examined without finding peats or soils 

 within the till, or anything indicating an interglacial period in Maine. 



The relation of the marine clays to the till deserves special study. I 

 could find no fresh exposures showing the relations of the Waldoboro 

 moraine to the marine clay. On the surface the clay overlay the moraine, 

 but the base was not seen. At Sabatis Village the marine clays also over- 

 lay the terminal moraine, to a depth of 8 feet, but the base of the moraine 

 was not exposed. It is thus uncertain whether at the base the terminal 

 moraines cover the marine clays or not. 



