78 R. S. TARR 



clays formed in the same manner as those now accumulating. 

 They are believed to represent modern lake-filling similar to that 

 now in progress at the head of the lake. When the number of 

 torrential streams that descend the valley wall is considered, 

 the amount of lake-filling which this stratum represents is not 

 excessive. These streams have formed deep gorges, having not 

 only removed much drift, but also cut deeply into the shale. 

 The material thus removed seems ample to make this deposit. 



The upper series of coarse sedinie?its. — A much more difificult 

 problem is presented by the sand and gravel series, sandwiched 

 between" the two clay beds, and covering an area whose length 

 north and south is known to be over one and a quarter miles. 

 Some widespread change in condition is here represented, indi- 

 cating a stage during which clay deposit was interrupted, appar- 

 ently after the ice-dammed lake ceased to offer opportunity for 

 deposit of lake clay, and before conditions appeared which per- 

 mitted the accumulation of the later lake clays. 



This period of interruption of lake clay deposit must have 

 been one in which, at the site of the wells, the conditions were 

 either those of a shallow lake or else of absence of lake water. 

 Both the coarseness of the sediment and the abundance of organic 

 remains • indicate this. It is inconceivable that at a distance 

 of three-eighths of a mile (the distance from the outermost well 

 to the nearest valley wall) gravel and sand could be deposited 

 in a lake from 56 to 118 feet deep, especially at a point remote 

 from the mouth of any stream. It is inconceivable, also, that 

 gravel and sand could be deposited in such a lake over so wide 

 an area. Nor does it seem probable that such a large number 

 of logs would be accumulated in lake deposits. The chance 

 discovery of seven logs in boring thirteen six-inch wells through 

 this sand-gravel series indicates a large number of logs in the 

 series. This point becomes all the more striking from the fact 

 that only two logs were found in the recent lake clays, and both 

 of these near the sand-gravel series, while no logs were encoun- 

 tered in the ice-dammed lake clays. 



Professor Penhallow has determined the two specimens of 

 wood preserved as follows: (i) South Well, 30-35 feet in clay, 



