of the Blue Ridge three miles east of the "Wind Gap." The boundary here mounted and crossed the Kittatinny ridge sixteen hundred feet high, being well shown upon its summit, and then passed over the intervening valley to the Broad Mountain or Pocono range. The Delaware at the "Foul Rift" is elevated two hundred and fifty feet above tide; and where the glacier boundary crossed the mountains in the interior it was at about twenty-six hundred feet elevation on the highest land in Potter County, the Continental watershed. This vast glacier was so thick as to overtop even Mount Washington, for it dropped transported boulders on the summit of that highest peak in New England. Its southern edge in Pennsylvania was at least eight hundred feet thick in solid ice. A hundred miles back among the Catskills it was thirty-one hundred feet thick, and two hundred miles back in northern New England it was five thousand to six thousand feet thick, being still thicker farther northward. The Pocono Knob, near Stroudsburg, in Pike County, Pennsylvania, out-topped the glacier, and jutted out almost like an island surrounded by ice. The late Professor H. Carvill Lewis, who closely studied this glacier, has described how, all over the country which it covered, it dropped what is known as the "northern drift," or "till," or "hardpan," in scattered deposits of stones, clay, gravel and _débris_ of all kinds, brought down from the northward as the ice moved along, and irregularly dumped upon the surface, thickly in some places and thinly in others, with many boulders, some of enormous size. It abraded all the rock surfaces crossed, and transported and rounded and striated the fragments torn off in its resistless passage. The line of farthest southern advance of the ice is shown by the "Terminal Moraine," stretching across country, which put the obstructions into the "Foul Rift." A glacier always pushes up at its foot a mound of material composed of fragments of rocks of all shapes and sizes, which the ice has taken up at various points along its flow and carried to its terminus, thus forming the moraine. This "Terminal Moraine" has been traced and carefully studied for four hundred miles across Pennsylvania, showing throughout a remarkable accumulation of drift materials and boulders, heaped into irregular hills and hollows over a strip of land nearly a mile wide. The action of the Delaware River currents at the "Foul Rift" has washed out the finer materials and cobblestones, leaving only the larger boulders and rocks to perplex the navigator.