Sheet structure in New England granites tends toward parallelism with the exposed rock surface and is completely independent of all primary rock structures, commonly transecting contacts between the granite and xenoliths, roof pendants, the country rock itself, and minor postgranite intrusive bodies. In general the sheets become progressively thicker, flatter, and more regular with increasing depth. Evaluation of the possible causes of the structure indicates that relief, through removal of superincumbent load, of a primary confining pressure is chiefly responsible for the large-scale exfoliation phenomena involved. Insolation, the progressive hydration and formation of chemical alteration products in certain susceptible minerals, and the mechanical action of fire, frost, and vegetation are possible minor contributory causes. With insignificant exceptions, sheeting in northeastern Massachusetts and adjacent parts of New Hampshire, where detailed studies have been made, is preglacial in origin. Its attitude with respect to present topography therefore facilitates certain comparisons with preglacial topography and thus permits minimum estimates of the thickness of material removed by glacial ice from specific localities. Not only do the granite sheets or shells thicken with depth, but statistical data demonstrate a fair degree of quantitative consistency in this relation. The sizes of large granite boulders-and therefore of the respective sheets from which they were torn-thus furnish an additional clue to their original depth beneath the preglacial surface. Results of these studies suggest the removal of a blanket of rock and preglacial regolith at least 10-15 feet thick by glacial abrasion and plucking from the stoss, or north, slopes of most hills, and of a somewhat greater thickness from their east slopes, summits, and west slopes. Severe plucking and quarrying of the rock appears to have been responsible for strongly concentrated erosion on the lee, or south and southeast slopes of many hills to maximum demonstrable depths in excess of 100 feet.