470 GLACIAL GRAVELS OF MAINE. ' 



respect from the dead water that occupied the glacial channels north of the 

 hills, except that they were not confined within so narrow limits. (4) Thus 

 far I have not been able to find fossils in their sediments. Maine is so far 

 from the terminal moraines of southern New England that it will not be 

 surprising if it shall be found that the ice front retreated northward faster 

 than the land plants and terrestrial invertebrates could advance. More- 

 over, these organisms had just been wholly driven out of New England, 

 unless possibly on a few of the higher mountains and islands. West from 

 Staten Island the plants could follow the retreating ice by the shortest lines, 

 i. e., at right angles to the ice front. In New York and Pennsylvania it 

 would be much easier for them to accompany the ice in its retreat than 

 for them to travel obliquely after the ice northward and eastward all the 

 wav from New Jersey to Maine. Prof. B. K. Emerson has recently found 

 fossils in sediments of late glacial or early postglacial age situated in 

 central Massachusetts. It would require only a third as long for terrestrial 

 plants and animals to travel to tliat place as to Maine, and probably the 

 ice was all melted before they reached the latter place. If there was any 

 retreat for these plants and animals from the ice in eastern British America 

 it has not been reported. Reference is here of course not made to algse 

 naturally inhabiting snow and ice. 



VAIiLEY DRIFT. 



VALLEY DRIFT OF PURELY FLUVIATILE ORIGIN. 



In a country of hills and rather level valleys, like most of Maii:ie, the 

 surface Avaters erode the uplands, carry their load down the steeper slopes 

 of the hills, and then may or may not drop the coarser portion as they 

 reach the more moderate slopes of the valleys. In Maine the hills are 

 usually diversified by numerous small lateral valleys, sometimes due to 

 inequalities in the distribution of the till, but more often to the accidents of 

 preglacial Aveathering and erosion. Most of the surface waters of the 

 uplands are thus soon converged into valleys and ravines. Erosion by 

 surface waters must always have been most active in these smaller valleys. 



If the deep sheets of alluvium which cover the bottoms of the broader 

 valleys are composed of inaterial eroded from the uplands by surface 

 waters after the melting of the ice, we ought now to find a system of 

 ravines comparable in A^olume to the valley drift. The brooks that form 



