628 GEOLOGY OF OLD HAMPSHIRE COL^NTY, MASS. 



cuttings for the relocation of the tracks of the raih-oad running south- 

 west from Millers Falls gave time sections radiating out from the head of the 

 delta. Besides most instructive sections of kettle-holes, described further 

 on, the opening gave a fine view of the whole structure of the delta (see 

 fig. 41, p. 668). 



At a point near where the two railroads separate, the cutting was 20 

 feet deep and showed tlie sands resting on glaciated surfaces of gneiss 

 and diabase, without the intervention of till or clays. 



The section showed an extensive body of sands, often exposed 12 to 

 16 feet in thickness, and cross-bedded in great sheets which dip south away 

 from the head of the delta and represent the advancing front of the latter. 

 Above this a horizontal layer of gravel, averaging about 3 feet in thickness, 

 and diminishing in thickness and coarseness outwardl}', made the surface. 

 This represents the concentration gravel manufactured out of the cross- 

 bedded sands of the delta by the floods of the river as they swept over its 

 surface after its front had passed farther outward. 



Where kettle-holes had sunk during the flood time, this gravel thickened 

 below to fill the depression, and had jjlainly been pushed into the depres- 

 sions from the direction of the head of the delta, the gravels being cross- 

 bedded in their thickened portions, with radial dip. 



All along- the eroded front of the delta overhanging Turners Falls the 

 clays, resting directly on till or sandstone, rise to a height of 2.50 feet above 

 sea and are capped by the delta sands. The clays have a maximum thick- 

 ness of 59 feet and are thin-laminated, with the layers 1 to IJ inches thick. 

 The clays change upward into the sands by repeated alternations of sand 

 and clay. At the top of one stratum of clay 1 foot thick a single layer was 

 contorted and compressed into acute folds bent over southward and covered 

 by a foot of sand, as if moved by the friction of the waters by which the 

 thick layer of nonlaminated sand was brought in. All above and below 

 was undisturbed. 



The illustration, fig. 35 (p. 629), indicates the relation of the beds at 

 the large brick pit south of Turners Falls. 



The delta sinks southward into the deep land-locked hollow in which 

 is the -\allage of Montague, and along the bald face of the mountain to the 

 east of the callage the terrace is represented only by a narrow bench cut in 

 the till, and farther south cut in the high sands which fill the Mount Toby 



