GEOLOGY OF THE NORTHERN ADIRONDACK REGION 447 



trend closely conformis to the direction of movement of the ice 

 sheet, which mus;t thus have thoroughly scoured them, and it 

 may well be that some, or all, of them have somewhat of the 

 rock basin character, though no proof of this is yet at hand, s^o 

 far as the writer is aware. Many of them are demonstrably held 

 up by morainic dams; but that might be true and yet the lake be 

 siomewhat of the rock basin type. Many have highly irregular 

 shore lines, owing to the drowning of the mouths of the small, 

 tributary valleys, and in general there are no features of these 

 which at all suggest the hanging valley type; they rather 

 strongly suggest the contrary. In the comparatively small 

 number of instances of what may prove to be hanging valleys, 

 of which Bog river falls at the upper end of Big Tupper lake is 

 a good example, it is far from certain that the streams are not 

 locally out of their preglacdal channels near their mouths, and 

 that the fall is not thus toi be accounted, for. There are however 

 some features of these larger lakes that do suggest some deep- 

 ening of their basins by the ice sheet, but the data are too frag- 

 mentary to justify a present discussion. 



Many of the Adirondack lakes are being shallowed quite 

 rapidly by the considerable amount of sediment washed into 

 them by the streams. In the few thousand years that have 

 passed since the ice vanished from the region quite a number of 

 lakes, both large and small, have been completely filled in this 

 way and converted into vleis. And at the present day many 

 examples showing all stages of the process are to be found.^ 

 Some are converted linto comparatively dry meadows, some are 

 wet and boggy, some have still a foot or so of water, but with a 

 growth of vegetation over the entire surface, others have still 

 some clear water in the center, others only a fringe of rushes and 

 water lilies along their margins, still others are very shallow 

 throughout but with only a beginning of vegetable growth, and 

 this well out in the pond as well as near shore, yet others are 

 still comparatively deep. Almost without exception the topo- 

 graphic sheets of the region show examples, and often numer- 

 ously. On the Saranac lake quadrangle, for example, a filled 



lake basin, 4 miles long, is seen in the north center of the sheet, 

 ) 



'See Smyth. C. H. jr. Lake Filling in the Adirondack Region. Am.'' 

 Geol. 11:85-90. 



