368 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



like tliiit of the Holyoke range, tog-ether with small fragments of a white 

 rock, like the white trap described above (see p. 365), but not showing 

 pyrite or porous texture. I associate these disturbances, and similar ones 

 that appear beneath the posterior sheet as far north as the latter can be 

 traced, with the bed of white trap described above. They possibly rep- 

 resent the border of an explosive eruption of limited extent, whose tuffs 

 may have locally loaded the muddy floor of the estuary so as to have pro- 

 duced the crumpling of the beds, but the outcrops are insufficient to give 

 the whole history of the deposit. 



It may be noted that the small sills which appear a few feet below the 

 posterior sheet 90 rods north and 150 rods south of this area greatly contort 

 the sandstones, and the disturbances here noted may be due to the same 

 cause. 



THK 130UNDAKV OF THE LONGMEADOW SANDSTONE. 



The northern Ijoundai-y of the sandstone, in Gill, is very complicated, 

 because here at the northern, narrowed end of the central sand flats the 

 feldspathic gravel at times projected far out over the sands from the west 

 and the slate gravels from the east. The area of the sandstone narrows as 

 one goes down in the beds, so that in their undisturbed state the central 

 sandstone graduated east, west, and north into the two conglomerates, with 

 manv intercalated lobes; and now that they are tilted and faulted one finds 

 mail}' sudden changes from the straight, sudden fault boundaries to the 

 complex, lobed line of passage of sandstone into conglomerate. Especially 

 marked is the narrow band of fine, deep-red, shaly sandstone which rests 

 upon the trap and follows it north nearly to the fault in the latter on the 

 Turners Falls road. This suddenly-appearing and exceptionally fine-grained 

 bed seems due to the shallowing and obstructing of the bay b}- the out- 

 pouring of the trap. 



Because of the prevalent easterly dip of the rocks the boundaries of 

 the sandstones upon the arkose ^jresent along their western border the nor- 

 mal relations, and the arkose passes regularly below the sandstone. Along 

 the eastern border of the northern basin the sandstone dips beneath the 

 conglomerate, and it is proved to pass far beneath the upper beds of the 

 conglomerate, becatise it is twice brought up by faults and repeated upon 

 the western slope of Mount Toby, once at the 500- and once at the 700-foot 

 contour, as seen in the sectional view of the mountain on the section sheet 



