The pass we named Pinnacle pass, on account of the many towering pinnacles overshadowing it. Its elevation is about four thousand feet, and at the summit it has a breadth of only two or three hundred feet. The snow on the divide is greatly crevassed, but a convenient snow-bridge enabled us to cross without difficulty. The crevasses increased in breadth with the advance of the season, and on returning from our mountain trip in September we had to climb up on the bordering cliff in order to pass the main crevasse at the summit. Some idea of the crevasses of this region may be obtained from the following figure, drawn from a photograph taken on the western side of Pinnacle pass, not far from the summit. The cliff on the north of Pinnacle pass is really a huge fault-scarp of recent date, intersecting stratified shale, limestone, and conglomerate, with a few thin coal-seams. The strata dip toward the north at a high angle, and present their broken edges in the great cliff rising above the pass. The cliff, extend westward from the pass, and retain a nearly horizontal crest line, but increase in height and grandeur, owing to the downward grade of the glacier along their base. A mile to the westward their elevation is fully two thousand feet. The cliffs throughout are almost everywhere bare of snow and too steep and rugged to be scaled. They form a strongly drawn boundary line in the geology of the region, and furnish the key to the structure and geological character of an extended area. All the rocks to the southward are sandstone and shale belonging to a well-defined series, and differ materially from the rocks in the fault-scarp. I have called the rocks toward the south, the YaNtat system, and those exposed in the faces of the fault-scarp the Pinnacle sys-tem. Directly north of Pinnacle pass, and at the base of and Owen, the rocks of the Yakutat systern are exposed, and from thei’: position and a,:soeiation it is evident that they are younger than the Pinnacle system . and belong above it. If these conclusions are sustained by future investigation, they will carry with them!’ certain deductions which are among the most remarkable in geological history. On the crest of the Pinnacle pass cliffs I afterwaI.+Is found strata containing fossil shells and leaves belon:zing to spe:.ies still living. These records of animal and plant life sh,ov that not only were the rocks of the Pinnacle; system (lel )osited since living species of mollusks and plants came into existence, but that the Yakutat system is still more recent. More than this, the upheaval of the mountains, the formation of numerous 141-at-scarps, and the origin of the glaciers, have all occurred since Pliocene tintes.