MODIFIED DRIFT OF THE LAKE DISTRICT. 123 



The noticeable feature in the surface geology of these lakes is the ab- 

 sence of modified drift. Their shores are chiefly of coarse glacial drift 

 or till, with occasional ledges. The neighboring basin of Ossipee lake, 

 on the contrary, is characterized by very extensive and probably thick 

 deposits of modified drift, presenting a remarkable contrast. These de- 

 posits are also abundant in the Pemigewasset valley on the west. Their 

 conspicuous absence from these intervening basins needs to be accounted 

 for, and this seems to be due to different rates of progress in the depart- 

 ure of the ice. The later continuance of the ice-sheet over these lakes 

 turned all the drainage from the south side of the White Mountains into 

 the Ossipee basin and Pemigewasset valley, and even caused the modi- 

 fied drift, which was contained in this part of the ice, to be mostly car- 

 ried away. Our explanation of the remarkable deflection of strias on the 

 east border of these lakes is thus attested also by the modified drift, as 

 by a separate and independent witness. 



In describing the modified drift of this area, we will proceed from the 

 mouth of Winnipiseogee river to the Wiers, and thence northward, in- 

 cluding Squam lake, and passing around Winnipiseogee. The extent of 

 these deposits is shown on the general geological map in the atlas. The 

 interesting beds of clay and rarely of sand, overlaid by till, which occur 

 at numerous places about these lakes, constitute a peculiar class of modi- 

 fied drift found nowhere else in the state. The localities of ordinary 

 modified drift will be first described, and afterwards the instances of clay 

 or sand overlaid by till. An explanation of the probable mode of forma- 

 tion of these different deposits will then be stated. 



The mouth of Winnipiseogee river at Franklin is 269 feet above the 

 sea. Its fall in the last two miles of its course is 146 feet, and its whole 

 descent from the lake is 244 feet, (See p. 103.) The modified drift of 

 the Merrimack valley is well shown on both sides at Franklin, its highest 

 terrace being 150 to 175 feet above the river; but the Winnipiseogee, for 

 the last mile and a half before entering this valley, is bordered only by 

 till or ledge. The first area of modified drift that we find on this stream 

 lies between Cross's mill-pond and Tilton, extending about a mile along 

 the river and as far to the south, where it lies principally on the west side 

 of the railroad. This deposit of sand and gravel has a height 30 to 50 

 feet above the river, slightly exceeding the upper terraces of the Merri- 

 mack at Franklin. 



