668 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



hole (7) was much wider and only the northern border is di'awn, showing 

 the horizontal sands breaking off abruptl}' and sands with steep southward 

 dip carried in to fill the cavit3^ The outcrops of trap and gneiss covered 

 with olacial strire, at the base of this section, show that the sands extend 

 down to the rock, and that no clay exists below them which might by lateral 

 flow have allowed the subjacent sands to sink down. Indeed, as the section 

 is cut in the center of a great sand plain, such a supposition is plainly 

 excluded. 



At 8 begins a general sinking of a broad area; at 9 an earlier and more 

 rapid sinking of a limited area, which was filled with gravels that are 

 finely cross-bedded with southerly dip, showing that they were carried into 

 the depression by a current from the north. Just below this j)oint the 

 New London Northern and the Fitchburg railroads separate, and at tlie first 

 cutting below the point of separation on the Fitchburg road the depression 



s 



10 FEET 



Fio. 41.— Section south of Millers Falls to show kettle-hole formed hy ice stranded on the surface of the sands. 



represented in fig. 41 was cut across, which is here given in order to contrast 

 a cavit)' produced plainly by the stranding of floating ice with the sink-holes 

 under discussion. 



The horizontal sands come toward the cavity undisturbed from either 

 side, and at a certain distance below retain their horizontality beneath it. 



Down the slope on the north side the sands are bent down and the 

 layers are combed over and disarranged, ending abruptly at the sui-fitce of 

 the cavity. Below the south side they are squeezed together and finely 

 con-ugated. A thin layer of gravel ai)pears thickened and irregular in the 

 bottom of the cavity and discontinuous on its southern side. The whole 

 was filled with a fine unstratified loess, wliether wind- or water-brought is 

 uncertain. 



Farther west, across the middle of the great Montague plain, runs tlie 

 line of large water-filled kettle-holes alreadv mentioned as indicatino- the 



