538 GEOLOGY OF OLD HAMPSHIRE COU]!fTY, MASS. 



iindecomposed and also largely siliceous. Small pockets of water-washed 

 sand occur somewhat rarely, generally as broad sheets less than a foot in 

 thickness and dipping often at a high angle. The}^ merge, often with 

 various contortions of their layers, into the normal till, and are plainl}' 

 remnants of deposits made by subglacial water seams, which were not 

 wholly molded into the common mass by the later work of the glacier. 



The exceeding compactness of the mass is a factor of prime impor- 

 tance in any consideration of the origin of the deposit, since it can be 

 explained only by assuming it to have been caused by the great weight 

 of the ice which rested iTpon it. For a long time I thought it possible to 

 exj^lain this as due to the slow compacting of a mass of loose material of 

 various sizes aided b}- the percolation of water, but when once dug up and 

 thrown in heaps it becomes compact again only when dry, as does also 

 the Champlaiu clav, which lies above it. When water-soaked, however, 

 it sinks readily into fine mud. When both are in their original position 

 and have not been disturbed and are still permeated with water, one can 

 easilv push a cane several feet into the clay, but could scarcely penetrate 

 the till more easily than the sandstone. Where this till is well developed 

 a workman will often not remove more than a yard of it in a day. In 

 digging the cellar of the Amherst House the attempt was made to split it 

 olf in blocks by means of large wedges and sledges, but the best steel 

 was rapidlv blunted, and these were abandoned in favor of powder, and 

 the mass was blasted out as if it had been a rock. In digging a well at 

 the residence of the late President Clai'k it was also necessary to blast 

 in the same deposit. Masses of the till brought up from a depth of 55 

 feet from the well sunk at the first house south of the Amherst College 

 o-rounds, where the whole excavation was in the typical bowlder clay, 

 could be trimmed into hand specimens with the hammer while still fresh, 

 and broke with a smooth, broad conchoidal fracture, like flint, and pro- 

 jecting pebbles would be broken by a blow without being dislodged 

 from then places. Near the bridge in Leeds an excavation made several 

 •years ago exposed a vertical wall 30 to 40 feet high, and it has since 

 scarcely crumbled at all. The deep railroad cutting south of Leeds and 

 the steep eastern bank of the river at that place are also good examples of 

 its durability. It is characteristic of the valley di'ift no less than of the 

 upland drift already described that it is a wholly amorphous and unstrati- 



