556 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



bed mifrht well have been obliterated, I am inclined to think tliat such a 

 second layer was deposited on a second till. At the same time I explain 

 this second layer in the cellar section as a sheet of sand which originally 

 formed a part of the lower stratum (2), and which, when frozen, was moved 

 as an immense bowlder into its present position. Thus it would be classed 

 with the true sand bowlders — regular flattened elipsoidal sand pockets with 

 their longer and shorter diameters averaging about 8 and 4 inches, respec- 

 tively, which occur not rarely in both the upper layers of the till, and 

 which can be explained only by supposing them rounded to their present 

 form when compactly frozen. 



Another curious phenomenon which points in the same direction was 

 observed near the south end of the west wall of the cellar. A fissure had 

 opened an inch and a half, commencing at the upper surface of the sand 

 layer and running down through the middle drift layer and for a little way 

 into the lower sand stratum, and this tissure had been filled with alternating 

 layers of clay and sand, about seven in all, which correspond on each side 

 of the center and present a curious imitation of a mineral vein. (8ee figs. 

 4, 5 of PI. XII.) This would seem also to find its explanation most natu- 

 rally in the assumption that the sand layers (2 and 4) were frozen when the 

 fissure was formed and that the latter was kept open so long that successive 

 layers of muddy water trickled down tln'ough it. The sand bed abounds in 

 small masses, 1 to 2™" in size, formed of a few grains of sand cemented with 

 liraonite. 



Tlie upper \-Ajer of the till (5) difiers in no respect from the lower, and, 

 like it, was removed with chisels and heavy sledges. It had a thickness of 

 5 feet in the section, but the ground had been lowered here by the same 

 amount, so its whole thickness was more than 10 feet as it appears a few 

 feet west of the cellar. The massive and compact character of the stratum 

 was shown by the effect upon it of the extreme cold of the Avinter of 1879. 

 The mass above the sand expanded with the freezing so energetically that 

 it projected like a cornice 10 inches in the west wall of the cellar, which 

 had been cut away vertically. 



I am thus inclined to explain the phenomena I have described by 

 assuming that after the deposition of the first till there was a retreat of the 

 ice, during which heav}^ sand beds were deposited in the valley, followed 

 by a second advance of the ice, which then plowed up and destroyed the 



