117 individual outcrops of each group are in many instances lithologically similar. In the southern part of the map-area the contact has been placed below a band of conglomerate exposed west of Uslika Lake and on Thane and Vega Creeks, and containing pebbles of banded tuff and of intrusive rock not unlike that composing some of the pebbles in one of the bodies of conglomerate in the Lay Range. In other respects these conglomerates are not at all similar. The conglomerate west of Uslika Lake lies above a fault or a pronounced angular unconformity. On Tutizika River, and down almost the entire length of Lay Creek Valley, a well-exposed fault zone is believed to mark the contact. METAMORPHISM Almost all these late Paleozoic rocks are composed in part or entirely of volcanic material; the andesitic flows, breccias, tuffs, and greywackes have been altered by the processes of chloritization, propylitization, and saussuritization to aggregates of chlorite, sericite, epidote-clinozoisite, clay- like matter, and minor calcite and pyrite. The change appears to have been essentially one of introduction of water, with some sulphur and carbon dioxide, to the rocks. The dark minerals have been most severely altered; in nearly all rocks the pyroxenes have been almost completely changed to amphibole, or chlorite, or both, and in many specimens the original presence of phenocrysts of pyroxene or amphibole can only be recognized by the occurrence of crudely polygonal clusters of chlorite, needle-like amphibole, and grains of clinozoisite. The feldspar crystals are more resistant to alteration in these rocks, and in a few specimens are quite fresh; most of them, however, are partly to completely saussuritized. In most rocks phenocrysts and groundmass appear to have been about equally altered. The intensity of this alteration does not appear to be related to any of the recognized shear and fault zones, or to the numerous bodies of intrusive rocks, but is mainly restricted to volcanic material, and seems to be a normal autometamorphic process (propylitization) consequent on consolidation and cooling of the voleanic matter. The presence of pro- pylitized fragments of andesite and tuff in greywackes containing recog- nizable organic remains suggests that the alteration took place in each flow and tuff bed individually, as it consolidated, before its fragmentation and transportation to the greywacke bed. That the alteration was facili- tated by solutions that circulated along joints in the rock is indicated by the abundant coating of serpentine-like material, some of which is typical antigorite, on fracture surfaces. The larger fractures apparently did not serve as channelways for widespread movement of the solutions; very few shear zones are serpentinized. The rocks of non-voleanic origin are fresh. All the limestones are partly recrystallized. The sandstones and grits are composed mainly of metamorphic materials, and have been unaffected by any processes to