544 THE POPULAR SCIENCE MONTHLY. 



glacier in what is known as a terminal moraine, which in many cases 

 stretched completely across the valley and marks the place where the 

 terminal face of the glacier was stationary for a considerable period 

 of time before it melted away, and allowed the water to accumulate 

 in the space once filled by the ice. These glacier-built dams are to 

 be met with in all countries which have been subjected to glacial 

 action, and are especially well marked amid the Alps and in Scotland, 

 where they have been most thoroughly studied, on the Scandinavian 

 peninsula, in the Northern States of the Union, and amid the southern 

 Alps of New Zealand. As the bottom of the valley in which such a 

 lake is formed is usually worn deeper by the action of the glacier 

 during the formation of the terminal moraine, this second form of 

 lake-basin is quite often combined with the first. 



To this second class also belong the thousands of little lakelets 

 scattered over the Northern States, which are confined on all sides by 

 banks of drift-material, and fill nearly every depression and hollow in 

 the huge banks of glacier-worn debris known as till, Tcaims, eskers, 

 etc., scattered so plentifully throughout our Northern country. We 

 have seen many of these pretty little lakelets through New York, 

 Ohio, and westward. Near Plainfield, New Jersey, scores may be 

 passed in a morning's walk. At the latter place they occupy the hol- 

 lows and dells in the drift, which is there of great thickness, and 

 formed not only from fhe Triassic sandstone which underlies it, but 

 also to a large extent from the limestone and gneiss found in place 

 only in the northern portion of the State. Intermingled with these 

 are many blocks of the peculiar reddish conglomerate found in situ in 

 Morris County, which show unmistakably the direction from which 

 the drift has traveled. Many of these stones are glacier-worn, and 

 have without doubt been transported from their northern homes by 

 the agency of ice ; not in one or two isolated instances, but in sufficient 

 quantity to cover the country for miles in extent. These little lake- 

 lets, becoming filled with vegetable matter, form peat-bogs, which 

 promise to become of considerable agricultural value in the future ; 

 these peat-bogs not only contain many wonderful things for the eyes 

 of those who are fortunate enough to possess a microscope, but also in 

 them are sometimes found the bones of the huge mastodon, which at 

 no very distant time inhabited this continent. 



3. The formation of lakes by a sinking of their bottoms, although 

 at first sight seeming to be the simplest and most common mode of 

 their formation, is really the most unusual. Lake Superior is de- 

 scribed as filling one of these depressions, as the rocks on its shores 

 are found to dip toward the centre of the lake, and the basin seems to 

 have been formed by a subsidence at that point, although greatly 

 modified in after-time by the erosion of the ice during the glacial 

 period. The valley into which the Jordan empties is another such 

 region of subsidence. 





