150 THE ICE AGE IN NORTH AMERICA. 



teristics of the great lines of glacial drainage extending to 

 the south of the glacial limit, and of which more particular 

 mention will be made in a future chapter ; but it was here 

 that we first detected the exact relation of these lines of gla- 

 cial drainage to the great ice- movement. Coming up from 

 Warren toward the glacial boundary, the valley of the Cone- 

 wango is seen to be filled increasingly full of gravel deposits 

 arranged in terraces on either side of the small stream. The 

 height of these above the stream is sixty or seventy feet. At 

 first the gravel is rather fine, but is constituted largely of 

 water-worn granitic fragments, which could have come with- 

 in range of the stream only by glacial transportation from 

 the far north. On proceeding a few miles farther north, 

 these terrace deposits become more and more irregular, being 

 thrown up into great ridges, and at the same time the mate- 

 rial becomes less water-worn and much coarser. Below this 

 point we had searched diligently in the gravel for scratched 

 stones, but none were anywhere to be found. A mile or two 

 from Ackley, however, we began to find pebbles upon which 

 the glacial scratches could be dimly traced. They had been 

 partially water-worn, but had not been rolled far enough to 

 completely obliterate their glacial marks. Upon reaching 

 Ackley, we found the whole valley occupied by a true gla- 

 cial deposit, terminating abruptly to the north, and through 

 which the stream had cut a narrow channel. The moraine 

 ridge, or dam, as we might call it, rises from 100 to 150 feet 

 above the present bed of the stream, and is equally well de- 

 veloped upon both sides. Scratched stones and granitic frag- 

 ments abound, and it is well marked upon either side of the 

 creek by the characteristic kettle-holes. Above Ackley, for 

 many miles, the Conewango pursues a sluggish course, and 

 is bordered by extensive marshy land. The explanation of 

 all this is that the ice-front remained for a somewhat pro- 

 tracted period at Ackley, allowing the large accumulation? 

 immediately below to take place. But its retreat from Ack- 

 ley for many miles northward was too rapid to permit of any 

 marked terminal accumulations: 



