111

ROCKS IN TUTIZIKA RIVER VALLEY

In the relatively low area extending northwest from the southern
mountain group to the southeast end of Lay Range, most outcrops show
banded tuffs and intercalated flows. Probably more than twice as much
tuff as flow rock is exposed. The section exposed in the valley of Tutizika
River reveals a relatively large proportion of argillaceous rocks. An
observed section on the north bank of the river and along one of its
small tributaries is as follows:

(Top of Section) Approximate thickness

Feet

Andesite, sheared, serpentinized, carbonated ............ceceeeeceees 100
Banded tuff; minor agglomerate; a few bands of highly altered

{iloNy7 | IRAE "5 Ghodne boasuonoDous dou oad bodADO dO GbDONDODDUOGOOOUGS 1,200
Argillite, dark grey to black, slaty, in part graphitic, pyritiferous,

COGAN TS ONC AN arias SRT SOME OO Oe a SEG od ol ob daE EE Ee 400
Argillte; intimately intercalated greywacke; altered tuff; andesitic

GOWER dade AB SRE Sd CSR RE GOS ROU enone DO cao RSD neTnat Gann SU BeBEDO 500

Chert(?), pale grey; minor tuff; argillite .............cccccccccccncce 100
Slate and argillite, blue-grey to black, in part calcareous, in part

uffaceoussiaminon Chent ste... can «bce skids Heian cate see ee 1,200
Banded tuff; about equal amounts of andesite flows, in units 25 to

TOO RLESG SEH IC kee ae repsstreyaietss stag sche so5 os Tas ne Saas ish So eNe soja gS eT meio 1,000

Total thickness .........eceeceeees -- 4,500

The highest members in this section are sheared, and local alteration
has developed much serpentine in the andesitic rocks and graphitic or
ankeritic material in the argillaceous or caleareous sedimentary rocks.

ROCKS IN THE NORTHERN MOUNTAIN GROUP

The most complete exposures of this map-unit are found in the northern
mountain group, which includes the entire Lay Range except for an area
of about 25 square miles near its southeastern end, occupied by an ultra-
mafic stock. Here, as elsewhere to the southeast, the strata of this map-
unit are characterized throughout by conspicuously banded tuffs. In the
Lay Range, however, they contain in addition a greater variety of non-
banded tuffs, greywacke, and non-volcanic sedimentary material. Two
typical sections, one in the southeastern and one in the northwestern part
of the range, are about as follows:

Section at Polaris Creek

(Top of Section) Approximate thickness

Feet

Banded tuff; interbedded argillite, black, slaty 500

Banded tuff; minor andesitic flows ...........sscecceccecerctcccvees 2,000

Banded! tufts minonrargillite: sashes  ctatevinersieteielsloieieleleic slcteialtielsheitieie ayelersta ore 600

Banded tuff; minor andesitic and basaltic flows 4,500
Limestone, blue-grey; tuff, red, massive; banded tuff; conglomerate;

sandstone; grit; greywacke (includes Lithostrotion horizon) ...... 1,200

REMI SA tLe one esha eee ae See OURS Fetes Dl aee alelavels ale siaralame tate at stovetsie:e 1,600
Banded tuff; interbedded agglomerate; minor andesitic and basaltic

FSTOC CIA MET CVA WLC KOg oh aiorcyccevallavoicnapsyer (oth vanete ai0/ ofp -fakols: «\oaefotaaeetese eile (aj oie 2,500

Banded tuff; intercalated porphyritic andesitic flows................. 4,000

Total thickness ............ 16,900