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