472 GEOLOGY OF OLD HAMPSHIRE COUifTY, MA8S. 



layers darkened by fine tuffaceous material. Twelve feet above the trap 

 the coarse tuff begins to appear in the sandstone, and this is its most 

 southern occurrence. 



It seems to me probable that the mud was swept over the still plastic 

 trap and sank into it to make the streaks of sandstone, and that the trap 

 was thus frothed up to make the amygdaloidal and cavernous structure. The 

 formation of the calcite, anhydrite, gypsum, and hematite all took })lace 

 immediately after, under the influence of heated solutions from the still 

 heated trap. The pyrite of the trap furnished the sulplniric acid for the 

 anhvdrite, and little calcite developed in the heated cavities of the trap 

 and gypsum and mi;ch calcite in tlie cooler fissures in the sandstone, while 

 abundant hematite and some magnetite impregnated the sands and formed 

 the beautiful surfaces of specular iron. 



In the bluff section to the north, mentioned on page 470, tlie vertical 

 south wall of the hill shows an exactly similar amygdaloidal band, about 

 12 feet thick, filled with wholly similar twisted sheets of sandstone and 

 shale. Indeed, at one point a block of sandstone at least 3 feet thick and 

 10 feet long is half included in the trap and half projecting. It is twisted 

 and baked gray and fissured all to pieces at the surface nearest the trap, 

 and is reddish at the center. This porous band of the trap is, however, 

 not, as in the quarry just south, the surface layer, but forms the base and 

 is covered by about 20 feet of coarsely columnar compact trap in the ver- 

 tical wall, and the thickness of the whole bed vipon it is much greater. It 

 can be seen to rest upon the fine-grained reddish sandstone below. It is 

 very porous, especially around the included fragments, and this porosity 

 runs out gradually in the compact trap above. One must put emphasis 

 u})ou tlie fact that these are thin sheets and films of thin-bedded shale, 

 often twisted in the lava and presenting shapes whicli can not })ossibly be 

 explained as inclusions of a solidified sandstone torn off from the surface 

 of the fissures up through whicli the lava passed. 



One may imagine the lava flowing southeast from the great vent at 

 Little Mountain, over the sand flats under several hundred feet of water, 

 for the most part cased in solid lava and thus producing very little effect 

 upon the ground over which it flowed and being very little influenced by 

 the water. If, however, the crust were locally ruptured and the liquid lava 

 came in large quantity into contact with the water, a violent iqtrush of 



