5.

6, _FEGIONAL GEOLOGY

IN THIS PAPER, THE REGIONAL GEOLOGY 1S DESCRIBED ONLY BETWEEN
58° ano 60° NortH Latituoe. HERE, THE DEVELOPMENT OF PALEOZOIC ROCKS 15
MUCH GREATER THAN IN THE REST OF THE PROVINCE. THE OLDEST ROCKS, BELIEVED
TO BE PRE-CAMBRIAN, ARE SCHISTS AND GNEISSES, EXPOSED IN THE Rocxy
Mountain TRENCH AND, LOCALLY, IN THE CASSIAR MOUNTAINS. THESE ARE FLANKED
BY Lower PALEOZ01C SEDIMENTS, WHICH FAN OUT NORTHWARD 7O INCLUDE MOST OF
NORTHWESTERN YUKON. EAST OF THE Rockies, THE PALEOzolcs ARE COVERED BY
THE Mesoz01c SEDIMENTS OF THE INTERIOR PLAINS. GOING WESTWARD FROM THE
Rocky MounTAIN TRENCH ACROSS THE CaSsIAR MOUNTAINS AND THE STIKINE PLATEAU,
THE Lower PALEOzOIC SEDIMENTS ARE PROGRESSIVELY OVERLAIN BY Upper Pateozoic
AND Lower Mesozo1e SEDIMENTS ANO VOLCANICS, THEN BY UppPER Mesozo!c SEDIMENTS
ANDO, FINALLY, ASOVE AN EROSIONAL UNCONFORMITY, BY WIDESPREAD TERTIARY

VOLCANICS. ALL THESE ROCKS, EXCEPT THE TERTIARY VOLCANICS, HAVE BEEN GENTLY

FOLDED ALONG NORTHWESTERLY-TRENOING AXES.

THERE WERE TwO PERIODS OF IGNEOUS INTRUSION, THE FIRST
DURING LATE PaLeozoic or EARLY Mesozolc TIME, WHEN ULTRAMAFIC ROCKS WERE
EMPLACED ALONG BOTH FLANKS OF THE CASSIAR MOUNTAINS AND IN THE NORTH
CENTRAL PART OF THE STIKINE PLareav. .Twese ULTRAMAFICS APPEAR TO BE
CONFINED TO Upper PALEozoic or Lower Mesozoic ROCKS AND TO HAVE BEEN
FOLDED WITH THEM. THE FOLDING PROBABLY TOOK PLACE DURING THE WIDESPREAD
OROGENY LATER IN MesozOlc TIME, WHEN THE COAST RANGE AND CASSIAR BATHOLITHS

WERE EMPLACEDO. 3

DuRING THE PLEISTOCENE, GLACIATION WAS WIDESPREAD.
DisSRUPTED DRAINAGE, RECENT CANYONS, GROUND MORAINE, ESKERS ANO KETTLE

TOPOGRAPHY ARE COMMON IN THE VALLEYS, WHILE REMNANTS OF VALLEY GLACIERS