A bed of tuff is composed of fragments of volcanic rock more or less sorted and transported by the action of water and whose fragments, having been cold when they were brought together, have produced no caustic effects upon one another. I know of but one important bed in the Triassic of New England which exactly fits this description. This bed I have called the Granby tuff. Its outcrop starts with the Belchertown ponds southeast of Amherst and runs parallel with, and a mile south of, the great Holyoke trap ridge, 12½ miles to the town of Holyoke.
In its eastward or shoreward portion it is enclosed in the coarse shore sandstones; in its central portion it is included in the fine sands of the deep water, and a t its south end rests for miles on the upper trap sheet.
At its bend near the gap where . . .