The I Niskzn-Chinitna Peninsula District, Alaska

Bulletin- 789

THE I NISKZN-CHINITNA PENINSULA ANDTHESNUGHARBOR DISTRICT, ALASKA

FRED H. MQFFIT

ENITIFXI RTATEB OQVERNMmNT HtEF1TlSG OFFICE: WABHINGMN 1P27 _\DDfTIONAL GOPIE8 or 'IH1B PVBLICATIOLf HAY BE PIIOcrn~mom TBE WPgBmHDmT OY OOV%BNYENT mmm om WAEHWBMH, D. C. I AT m CENTe PER OOPY CONTENTS

Geopphy-,---,,------.------,,----c B The c~astZina.------.--~--~.,-~-----,--,--

Darimge,,,,--,-r-,--I.------.,I------,------Routes sad t&------,------+- Timber and vegetation,, ,, , ------.------,------Gsme-,,-,,,------,------,,------Mriptiva lo^------,,------,---,--- Strati~phy-~------~~----,-~------,- Fol-mntCona in the area-, ,, ,, ,,------.------bwer Judc(7) rocks- - --,-----,.. , ----,- -,-,-,, - ,,, Middle Jureeaic rocked, - -- ,,-,------.---- Tu~ednisandstOne------,,,-,,-,,------.-~-- Character and dietrCbution -,,---,-*-- -. -,, Thieknem and structure-- ---.-----,-,.,-.,---- Aee and camlation-, ,,-,-- --*------,------

Intm~iverocks in the Tunedel %~ildstone--:I, . - Uppet Juras~licrcrcka------,,,.__-,------,------ChinitnasMe-----.I------,------d-+-- Character and di~tributlon--, ,- ., - .- - - - - ,--, - -, Thicknsm nnd dructum l---,,.------,.I------Age and correlation,, ,------,------

Mdnek formation- - - - A ,------. -- ---, ,,-,- ,,- - -- Character snd subdividona ,,-,,,a,,-----,-,-,, C hisik conglomernEe member- - - -,- - - - -., , ------Lithology----,..------,--,---,-,,-,--,,* lntrrrdcd igneous rocks, ,-----.,----,-,,-----,-

Ape and cordation- -,---,,ti+,------:a*-- Quaternsry deposlte- ,--, ---, ------.-- -,-,,,- --.,-. -, 8tmcture-- ,, -,------,- - -.---, ,,------,,,,:- -- ~saiod~hi* ,,,,,,-,-,,+----,,------,-,,,---,------, Mineral mourn, ,------. - ---+,, .------,,,------PehoIe~m,,---,.-,-,---,------,~------~~-, 8eew---,.------.,------,-.----,---. . Explorstion and dtlllhp- -,- ,--- -- .- ,,---,, .------,,-1, Character of the oil - - - , ------,,, - - - -,------,- - - -- Occurrenae of petroleum, ------,,------. , - ---,.,,-- --- Condition~in the vicinity of Tuxednf Bay (Snug Harbor) ,, Tmn-*----,---*,-.---~------~------,--,* Other minerals- -- ,----,-.,,--,,,,,-- - --,------* --- - m CON-

The Snug Harbor dimtrict, Alnaka- ,--,------,--,,,-,,,,---.- Intrduction,,,,,---,----,,-,,------,,--,-,,---,----,,,,-. Location ~rndarea-, ,,, ,,------,---,,,---,- OutZine of geogrsphy,,,---,--.----,-,,----,------,-,,-- kriptive -logy ---,,,--,.------,------,,------Stratimphy-,,,----,.---.,-_,,------,,++------Character of the rooks- ,,, ,-- , - - --,,,--,------_ - --- .

Lower Jude(I) mkar-, ---,-,,--+------, Middle Juraeeie mob,, -,-----,---"------Tuxednisandatone-.--.------,------Upper Jurasaic sockg--- .,-,.------Chinitna shale- ,--, .-, .,,- ,- - ,- - ,------Nskoek fom~tltion,----,-*------+------+------Tertiary rock~-----,,--,--.,-----,,-----_----- Quaternary deposit@-,, , , , , . . , , ------Btructure-----..:------,------,,-..,------Historical and economic geology ,,,.--,,-,..--,,-.,,---,------

Index --2---u------*------,I ------

ILLUSTRATIONS

lm Ptam 1. Tcqmgmphic map aP the InfaBln-ehinitna Peninsula ,,,,,,, In pocket. 2. WlogIc map of the Inhkh-Chinlha PenInmIa--,-,-,,,, In mket. 3. 'Pomphic map of the Infskln Bay-Snag Rarbqr disMct, In pock~t. 4, Ceol&c map of the Inlwgln Bay-Snug Harbor dlhtrict-,-,, 3n pocket. 5. A, Vlew to Lhe aonth Ln Park Creek Valley; R, Oil Bay and Inlakin Bay--,-,------,,------4 6, A. View toward the eat& ncroas Fit5 Creek Valley; 3, Bteeplg dipping Weof Chiuitaa shale and Nnlrnek formation on the ~011thaide at the entrance to Chinitna Bey------, -,,,,,,, 4 7. Sketch map show in^ dhtribntlon of timber betwen In- and TuxNnI Raya,,-,-,------,,--,------,-- FE :- 8, A, View of 011 Bay, showing the white Maknek beds overlytug the ChbItna ~h.hakon the east shore: B. Mountah on the *A east gfde of Oil Bay tram a polnt mrthe snmmft of the road to InE~klnmy,,----,----,------,------,,- 10 - 0, A, Mount Rleanor ; B, W&ward-Bippkg lwd8 in the lower part . of the Tuxedni anmtsbne haw a mile east cd Rlght Arm-,,, 10 + 10. A, View up lnfekln Bny from a point near the end of the wagon rond to 011 Rag; 8, View to the sonth and east amow tbe mud ants at the bead of Chlnltne Bag --,,----,-,,-,-----,,10 11. A, North end of Cbblk lel~nd,from Fmdl Point; B, Mmt -a, from Johnaen River, about 3 mllw iks mouth-- 68 Fmum 1. hdex map ~howhgWk Inlet, the Xni~kin-ChinibFenin- anla, and the areas reprmented on Platen 1, 2, 3, and 4----- 1 THE INISRIN-CXTKNITNA PENINSULA, ALASKA

5. INTRODUCTION The amdescribed in this paper (see fig. I) is on the west side of Cook Inlet between Iniskin and Chinitna Bays. It is a peninsula

Rmp. 1.-Inh map of th Cwk InJet redon trlrovfns the lnI&lm-CUdDt Pml11- suk and Cbe area rpp-ted on PSstetz 1, 2. 3. and 4 that has an area of abut 130 square miles and is separated from the maidand momtabs on the west bp a narrow Palley which extends from the Right Arm of Iniskin Bay nt>rtheastw~rdto the head of Chinitna Bay. For conaenierlce this ares may be cdld the Inisgin-Cbinitna Perkmila, Oil Bay, on the south side of the peninsula, is near the ietemection of parallel 59" 40' north latitude with meridian 153" 20' west longitude. Seldovia, on the southw~stend 1 of Kearsi Peninsula, is directly across Cook Inlet from Chinitna Bay and is the nearest white ~ttlementand the nearest post office except that at Iliamna, a native village on Iliamna Lake. The west coast of Cook Inlet has never had more than a scanty white population. It does not abund in furharing animals, has not attracted many prospectors for the metals, snd, wtiL recently hai had n6 canneries. The vicinity of Oil Bay, however, at one time received eonsiderabls attention because of the petroleum wepages found there and was the scene of drilling for a number of years. Shortly before the Alaskan oil lands were withdrawn from entry in 1910, the oil properties were abandoned, and no further attention was paid to them until the new leasing law was passed in 1920. This law renewad interest in the district, so that much of the ground ,was mstaked, and it accordingly became necessary, in order ta carry out the provisions of the law, to collect information regarding the areal geology and structure of the area likely to be prospected for oil. This report, which is ,based on topopphic and geologic surveys made in 1921, includes the information thus collected. Altbough this paper deals particularly wikh the geology of the Idiskia Penhula, it also contains an account of the field work in the vicinity of Snug Harbor in 1920. A separate section (pp. 57-70) describes the areal geology of the Snug Harbor district, but the ccmclusions relating to the possibilities of obtaining oil or other minerals in that district are stakd together wit11 those regarding the Iniskin-Chinitna Peninstlla on pages 6446.

PEEVIOUB WORK Oil Bay was visited by Martin in 1903, when the work of drilling for oil was in progress. This visit yielded the first report on the pibilities of obtaining oil in the district, based on field invdipa- tion by the United States Geological Survey. In the following year Stanton and Martin studied the geology of the west coast of 'Cook Inlet and the MasIra Peninsula from Tuxedni Bay to Cold Bay and in the murse of the summer visited Chinitna, Iniskin, and Oil Bays, whem they csrefully measured and studied in detail sections of the Mesozoic sedimentary rocks. These sections, with others measured on the Alaska Peninsula, form the basis of much that has since been published on the Memzoic stratigraphy of this part of Alaska. In 1909 Martin and Kata mapped the Iliemna region end

ZMartln, 0. C., The petroleum flelln of the Pacific coast ot Almh, with an ncconnt ot the Behg River coal dwits: U. I.Geol. Survey Bull. 260, pg. 31-49, 1906. .Itanton, T. W., and Martin, 0. C., Mesosoit nectlon of Cook Inlet and Alaska Peninmula: Gml. Soc. America Bull., vo1. 16. pp. 893-397, 401-402. 1905. a Martin, Q. C., nrld Kntz, F. 3.. A geologEc remnnaiasance of the IlIamnn reRton. Alasbn: U. 8. Geol. Survey Bull. 485, pg, G%74.'77-78. 1912. published w part of their report a discussion of the sections between Tuxadni and Iniskin Buys made by Stantan and Martin in 1904. From that time no further geologic mapping was done in this vicinity till 1920, when McKinley and Mofi t ' mde a topographic and plogic reconnaissance in the vicinity of Snug Rarbor. 93 miles north of Chinitna Bay.

The investigation whose results are here presented was made in 1921. It was undertaken with the object of mapping topographically and pIogidly the part of the west coast of Cook Inlet. that has the . grentest present interest to prospectors for petmleum and was re- stricted ta the peninsuZa between Iniskin and Chinitns Bays, except that the contiguous mainland and the north shore of Chiniba Bay wre included in order to round out the mBp snd join the work with that done in previous surveys. It was intended to publish a detailed map on a wbof 1: 62,500 (pl. 1), and this intention was carried out for the topographic map hut not for the geologic map. Owing to a strike of marine engineers only a part of the field force, without horses, wag able to leave Seattle and reach the area to be mapped a$ the beginning of the field seasom The remaining members of the party with the horn did not arrive till July. For this reason more p~'opssmaa made with the topopphic than with the plogic mapping, The field force consisted of two parties. one topographic and one geologic. C. P. BlcKinIey had charge of topographic mapping: He was assisted by Gerald Fitzgerald, topographic assistant, T. E. Jbhnson, Ellison Morris, A. H. Armstrong, and Ray Rnssell. The miter was in charge of the. geologic mapping and was assistd by -iY ,4rth11r-4. Baker, geologic nid. C. C!. Tousley, tTolnepL. Gray, md - C. P. Dyer. '3fcRinley with his party and two of the geologic party, includiiu Baker, landed at the cannery in Snug H~rborJune 2 and were taken by the cannery tender to Camp Point in Chinitna Bay the next day. The writer, with the rest of the men and 11 horm, arrived in Snug Harbor July 2 and in Chinitna Bng July 5. Field work ended for b0t.h parties August 29, for it was: nwessstry to return to Snug Har- bor in order to take the last bont of the season to Sesttle. The length of the field season was thus 87 days. Fine weather favored the work during June and the fimt meek of July, but during the re- mainder of duly and r\agtrst the rainy and clear days were about

'Moat, F. H., Oeolo~of the vkfnltr of Tmednf Bay. Caok lnlet. &&a: U. S. BmI. BWqBulZ 722, pp. 111-147. 1021, equal in number. This distribution of rain and fair weather prob ably represents the averap year md conhsts sharply with the unusually wet summer of 1920,

The peninsula between hiskin and Chinitna Bays has roughly the form of a aechr equivalent to somewhat more thm a quarte~ - circle, with its convex side turned to the southeast. (See pl. 1.) Inislrin Ray on the west and Chinitna Bay on the north are the - radii of the mr,and the curving coast of Cook met is the arc 3 of the circle included between the radii. The greatest dimension of the area is the chord of the arc, which runs from southwest to northeast ad is 1935 miles long. The part of the geninsdo, de- ~ribedin this report is limited on the landward or west side by 'a vdley, about 6 miles long, extending from the Right Arm of hiskin Bay to the head of Chinitna Bay. The maximum width of the area is thus about 10.5 miles. The curving coast line is in&rrnpted by indmt&tic)n~at Oil Bay on the =nth side of the peninsula md win a.4 Dry Bay a few miles s& of Oil Bay. 'The indentation at Dry Bay, however, is BO slight as hardly to merit the designation by.

The Iniskin-Chiniha Peninsula is nn outlier of the mountain range that extends dong the west side of Cook Inlet and down the Alaska Peninsula. Its prominent topographic features am a curving line of mountains that border Cook Met and determine the cod a extends line and lower ridge that northeastward from the w- east aide of Iniskin Bay to Chinitna Bay. Both of these topographic features are clearly determined by the geologic stmctum of the sedimentary be& of which they are formed. The mast mountains in general me higher than the interior mountain& Their altitude * decreases from 3,130 fat above sea level at Mount Chlnitna, nmr Cbinitna Bay, to 2,410 feet in Mount Pomwoy, between Inkkin and Oil Bays This ridge shows a steeper and more rugged face (ph.5, B, and 6, A) on the landward side than on the side toward Cook Inlet, for the seaward slope is a dip dope khat is controlled by the Light-colored rnrssive sandstones of the Naknek. formation. The scarp of the sandstone and the underlying bedg pmt- by it makes the steep inner slope of the ridge. Thia mas€ wall is broken through by Bowser Creek and Oil Bay (pl, 5, B),by I3rom Creek at Dry Bay (pl. 6, A), and by Bow Creek 3 miles northeast of Dry Bay. 1:. 1111~UA5' (l\ Cl~;~'l'l+:l

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IT. H. r.Pf11 11T.lr.41 -1-Ill F 1- lI1'1.l.ETIV 74'1 FT.A'P1: "

J 11 F-l\\ klltl llllLlml\~~I!f 11- I\ 11tI I 11z1l lr l'\lll all 1111 11 \1 11\1 s\\ll.ttl\f- I?$l.F,* \Ill I I $\I 41r f!la+lt'R \nil R~nllnpmns irr ttlr luwrvrotmd The ridge on the west side of the peninsule is straight and not sw, high ss that dong Cook Inlet. 3ta highmt point is 8,44!2 feet above sm leael, and its summits are smoother and more rounded. Be- ' tween. the two ridgea, in the central and northern part of the penimla, stand lower smooth-topped hills (pls. 5, A,, end 6, A), which occupy pnly a small portion of the whole arm. The principal valleys are tha straight, narrow valley leading from Right Arm to Chinitna Bay, lthe similar vaUep of Fitz and Bowser Creeks, parallel to the first, and the tramverse vnIleya of Brown and Bow Creeh. A shorbr transverse valley c~mectsthe Bowser Creek Valley with Right Arm.

Bornj hwn,and Fitz Creeks are the principal strssms of the district. They head near together in almost the exact centa~of the pninsula and with their branches drain of it. Bo-r and Fitz Cree& flow in opposite directions, the htinto Oil Bsy and the second into Chinitna Bay, but are in almost direct -ent and occupy valleys whose positions mincide with an anticlinal fold in the Tuxedni sandatone. Another smaller stream, Bow Creek, +hose valley is parallel to that of Brown Creek, dmh a consider- eMe aim east of Brown Creek. None of these creeh are glacial dreams, but they are fed during spring and early summer by melt- ing snows on the mountains and at that time carry much more water than later in the summer. Bowser and Fitz Cmh md the two smaller parallel creeks on the west that flow hto Right Ann and Chinitxla Bay occupy valleys whose direction and position are de- pendent on the principal lines of geologic structure in the district. The trmverse Palley bheen Bowser Creek and Right Am, the valley of Brown Crek, and the parallel valley of Bow Creek are apparently determined by a system of jointing and faulting that hns the same direction as the valleys. Them streams mpy rather wide, open valleys without canyons and with only minor exposures of bedrock. Their crmaller tribu- taries, on the other hand, are cutting.mrrow V-shaped valleys in the mft shales and in many places have developed falls and cascades on the hard conglomerate and sandstone bds interstratified with the shales. ROUIPES iCND !mAms Trard to Chinitna and Iniskin Bays is more or less inconvenient and at times is diflicult, for no boats call at parts on the west side of Cook Inlet. ,except during the summer, when, the camerg on Chi& Island in Tux& Bay is in operation, The wirest regular stopping place for Alaska steamers is at Seldovia, near the mouth 1-n-2 of Kachernak Bay. on the etrst, side of Cook Inlet. mstown is hmst 65 mih from Iniskin Bwy and is the nearest post ofice. 'me cannery on Chis& Maad is abont 60 miles by ses f mm Iniskin Bay and 26 milee from Chinitna Bay. It bas no post office, and there are no actommodations for travders except wch 5s are furnished thugh the conrtesp of the cannery people. hiskin Bay has dwp wafer and furnish= shelter fm large ha&, The anchorage, however. is nearer the west shore thm the east shore and freight under present conditions must tm discharged by lighter. This bay was formerly used at times by hab -king shelhr from storms while discharging freight in Ilia- Bay, but has- not been entend by the larger boats in recent years. Chinitnt~Bap is shallow in its upper sheltered part and is not nsed by large boats. The didrid under consideration is without trails. Wlmn drilling waa in progem at Oil and Drp Bays a wagon mad was built between Iniakin and Oil Bays for traaspo* supplies and equipment to the wells. There was also a trail from Oil Hay to Right Arm and another to Dry Bay. These trails have not been used in recent pears and are now grown up with alders and willows, so that in most plmthey are difficult to find. Where they ran through the timber and were blazed, or where they were @ed or had bridges bdtover the gulches, they mn be followed, but for the most part they furnish slight assistance, and in many places there is no sdvantage in trying to use them. The wagon road followed a creek from Iniskn Bay t;o the summit of the ridge betwem Iniskin and Oil Bays. This part of the road has beem entirely wmfied out, but the raminder, from the summit of the ridge to the csbin on Oil Bay, could be put in usable condition with- ouk great expense. A trd from Right Arm to Chinitna Bay wes originally used by the natives and doubtleaa was known to then1 long before white men came to this country. ~videitl~it was never used much by white men, for almost no traces of it are left. It is mid that there was once a *mil from Oil Bay or Dry Bsy to Chinitna Bay. Traces of mch la tmil were found on Fib Creek, bnt it is doubtful if this trail was ever usled much. None of these old trails exmpt the wagon md hmOil Bay to Inislrin Bay trnd part of the trail to Right Arm in the velley between Right Arm and Bowser Creek were of particular asshnce to the surveying parties in 1021. In most placm the parties found it quicker and better to wlsde.the streams and to cut trail only where that work WM unavoidable. This plan We8 open to the objection that in early mmer and akter heavy rains the streams were: high and dificult, if not dangerous, to follow. In the latar part of Au- gust, however, the larger streams were m low that they offered no dificrllty whatever, exeept where rlriftwd had ldged or where they were ove.rgrown by brush. All the streams are remarkably free from qnickmnd. In fact, soft ground, difficult for horns to t.rave1, was mnch less mmmthroughout the district than had been expected, for in most places the sand ~nclfine materid derived fmm the wwtherinp of the sedimentarlp formations was packed fidy.

An open stand of spruce and cottonwood timber ovem the valley flmps and the lower hill slopes of the interior of the peninsula, but is absent from the mountain dopes that face &k Inlet. (Sea pl. 7.) In addition ta spruce and cottonwoad there is a pdhof alder and willow. either of which may be found in the lower lands or on the hill slopes above timber line. As a rule the heaviest growth of willow ia on the valley bottoms near the streams or wet ground, for the willow requires much water. The densest growth of alder, on the other hand, is near timber line on the hill slopes. This vegetation, however, is not considered timber. Spruce and cattonwood are not uniformly distributed over the area in which they grow and are commpnly more or less weparated hm6 other. The timbered areas are interspard with parks overgrown by willow and alder or with tall paw, giving a most pleasing aspect to the landscape. (Pl. 5, 8.) Cottonwood thrivea along the stream courm, where it reaches a large size and forms extensive ,"roves, yet many lone trees are mattered along gu1cht-s above the valley bottoms. Seemingly the cottonwd 'is also able either to estsblish itself earlier or to maintain ihlf batter in many exposed, wbd-mwpt places than the spruce. Spruce timber is present in all the larger valleys but is larger and better in the psUeys of Bowwr and Brawn Creeks than dse- where. In the vicinity of Oil Bay (pls. 5, B, and 8, B)there are many fine, stmight spruces suitable for almost any use for which timber is likely to be needdl in this vicinity; Timber line in no place reaches nn altitude of 1,an) fwt and in only a few pllaces is as high as 750 fset. Good timber pwsnlm on the north shore of Chinib Bay in a place convenient for transportation, and for wveral years this area bas furnished piling for fish traps and the cannery pier in Snug Horbor. Grass of the variety commonly called '' redtop by Madam pm- pectore grow8 lnxuriraatly on the better-drsiaed Jand throaghout the district and furnishes abundant feed for stock. It mvem the " parks '" (pl. 9, B ) where it is not crowded ont by the willow or prevented from growing by wet ground and extends up the hill slopes (pl. 5, A) to the limit of nlders, making it difficult-toclimb the MIS in the later psff of summer and especially in tha fsll after the wed has formed .and the stalks are bent to the pund. Stalks of gram 7 feet tail are not uncommon after the seed paniclea have formed. Native p~ was cut nnd mred at Oil Bay for the homes during the years when the drillers were at work there. This district is not as abundantly sapplied with wild fruit as some parts of the inhrior of Alaska. Salmanberries, blueberries, and currants were found snd furnished a welcome addition to the fable. Blueberries are more plentiful than either salmmberrias or curfgnb. They are chiefly of the high-bush variety and grow best in the shaded timber areas in con&& with the low-bush berries, which grow in the open on the hill slopes above timber.

The west omst of Cmk Inlet in the viciniQ of Chinitna md Iniskin Rays furnishes only a small variety of animals and birds to interest the prospector and hunter. Brown and black hars are the principal larger animals. They are numerous and are p-nt ju all parts of the district mapped, so lthat carefal pmution must be taken against the low ~f fwd supplies that have to be left un- gua~ded. They are seen more fsequently in the gpring and aarly part of the summer than at other times, for they come out to feed when the vegetation first &arts and ere kss protected from view by the grass md the leaves sf the underbrush. The mhrshy flats at the head of Chinitna Bay are favorite feeding pounds for them in q~ng,so ththat it is not unusual to sea several at one time in the evening. After the salmon begin to a&nd the strams in July and early August the bears get much of their food by fishing on the rifflw where the fish are running or brg collecting the dead or dying fish along the banks. Their trails are found along all the fish streams, and the track of s big bear who crosses a, grass patch on the hilkide may be seen for waeks. The wolverine is the only other large animal in this didrict alp to molest a cache. He is universsmlly Zespised and dreaded because of his thieving habits, and mtil recently was countad as of no value as a fur-bearing animal. Thm are no moose, caribou, or mountain .sheep in the district, and fur-bearing animals are not nummus, so that trapping has not been particularly profitable. Expectation 6f the removal of restrictions on taking beaver, however, induced several trappets, to come into the.district and prepare to mt out trap linm. A few hair 4 am taken for their oil, which has an outside market as well as amalllocsl Ducks are plentiful in the fall, and a few ptarmigan and grous were seen by members of the rmrveying partiea in 1921. The number of ptarmigan and puse varies greatly from year to year, so that no single year gives a come& idea of their abundance or scarcity. Salmon begin'to run up the streams to their spming places in Jaly or the early p& of Angust in rtxordance with variations in the Mason or the spawning instinct. They are much less numerous than in many dreams of the Alaska Peninsnla and are reported to be les plentiful now than formerly, when the canneries were fewer. Rley are folIowed in their course upstream by great numbers of DoIly Varden trout, which faed on the salmon eggs and pay little attention to other fwd. A mlmon has an unappetizing appearance after the upstream journey is begun, and the trout is much preferred for table use. DESCRIPTIVE aEowaY STRATIU~ . WRMA'IIONS IH THE AREA The mEts of the peninsula between Iniskin and Chidtna Bay8 are almost exclusively marine sedimentary deposits, but ere composed of clastic material derived in 1srg.e part from older igneous rocks, among which granitic mk~were abundant. (Ses pl. 2.) The sedi- manta7 rocks are cut here and there by dark-colored dikes or are intruded by light-colored sills, and are separated by a great fault from tha vulmnic rocks (Lower Jurl~ssic0)of the mountains betweqn the heads of the two bays. In the order of their am, from the oldest to the youngest, they are the Tuxedni sandstone (Middle hassic) and Chinitna ahale and Naknek formation, of Upper Jurassic age. The kedni sandstone is composed of mndstone, arkme, conglomerate, md sandy shah and reaches a thihesa of possibly 7,080 feet. In the lower part of the formation the sandatone and other coam- &nd beds predominate over aha-le, but in the uppsr park ~hde predomhaes: ,wetly over sandstone. The shale commonly is more or less sandy, except at the top of the formation, where it is argil-, laceous instead of ammous and pdea into the overlying Chinitna ghde. Next above the Tuxedni sandstone is the Chinitna ahale, a fairly homogenmus formation of py,black, md ddish shales containing. subordinate sandstone and caIcsreous beds. Th;s formation is approximately 2,300 feet thick. The Chisik conglomerate, here treated as the basd member of the Nahek formation, overlies the Chhitna shala In its largest and mo& typical exposum in this area it is 290 feet thick and includ~ boulders and cobbles of igneous rock, especially granite.. It is, how- her, of variable thickness and character and throughout most of ills dhtriet either ie kepresented'by beds of grit and arbor is absent altogether. The part of the Naknek forhation above the Chisik mngtomerate member includes at least 4,500 feet of shale and mndstone, which are *.he youngat rocks in the district. Immediately above the Chisik member lies about 1,500 to 1,645 feet of shsle and subordinate sandstone. Thi~shale is overlain by 3.000 feet of beds of white or light- colored sandstone, which are the conspicuous clib-forming rocks (PI. 8, A, B) of the mountains bordering Cook Inlet in this peninsula. These formations succeed one another without structural uncon-. formiky, so far as is known. IdocaUy they are abundantly fwilifer- ow, so that their sge is well determind. The bds are folded rather closely on the northwest side of the peninsula near the volcenic rocks of the main mountsin chain of the mainland but are less compressed towhrd the east md dip in a pat

; ' ponocline beneath the waters of Cook Inlet. The strike in general is about N. $0" E. in the central part and west side of the penimla but is parallel with the coast line on the east and south sides and chanps from P3. 30" E. near Chinitna Bsy to nearly east on Iniskin . Deposits of gravel lie along the streams and on the maat, but bench gravels aad glacid deposits am uncommon. Erratic boulders of rock dfff~mtfrom the bedrock of the peninsula, however, bear evidence that the glaciers; brought in and left morainal material, but apparena y the gIcial deposik were mwor3red by strews or d~esea, so that typical glacial deposits are not seen. .The character and relations of these mh are summad in the following table :

TMCb Am =un UtbWa-r w= -(*t) Qosternary. msade@dwnd 4 1 Ohdd dam-: W, g.W md hmUa Wrs. =- M&w Ught-wloaad uandatoae, arkcm, BnB tuR. LBW (fray shsls rlth BBIL&U@ bdR. -1. MB C~z;~z~m~2&~me*m FalrIy hovar@lUumm mu, blsok. md CkMtMshak. reddish shales Kith uubor- cdmoua and 2,W areomus bob. hrenaocw~lgray sbsle with sabmdin& Ban- i- , ~&f$ooe M,rbslq -0 mmdstom, and mu- -rlnmnrute. Lorn JuraasIa vI v::ze,-m$~B~~~9Cwd&YI- mz.y The geologic map (pb 2) shows the areal distribution of the formations given in the table and also the principal structural feat-, together with structure sections. Because of the short field season and t$e purpose for which the map was largely intended, emphasis was laid on working out the p10gic structure of the possible oil-bearing Msrather hhan on mapping the boundaries of the formations, and for that reason mo& of the boundariee are not &own with an muracy comparable to that of the topographic baee map. North of Brown Creek as far as Mount Chinitna the boundary lines between the Tuxedni, Chinitna, and Naknek formations are shown only approximately and are so marked, but the line bet,ween the shale and the overlying ligh t-colored sandstone of the Naknek fomation is placed with mom ~cmacyexcept near Dry Bay. Most of the ofice work in correlating stratigraphic sections from different parts of the am,in constructing the structure sections and preparing the maps, and in studying thin sections under the micro- smp for use in this report was done by Mr: Baker.

Mount Eleanor (pl. 9) and the adjacent mountains west of Portage 6rdbetreen the heads of Iniskin and Chinitnn Baps sm on the lmrder of a belt of volcanic rocks that extends for many miles along the eastern side of the Chigmit Mountains and flanks the central granite mass. These volcanjc rocks am older than the granite and were intruded by it. They are mom resistant to weathering than the Jurassic sedimentary beds along the coast, and this fact, together with their manner of bmki into angular blmh dong jbint plan% haa given the area occupied by them a characteristic topography (pls. 9, A, and 10, A) that is usually recognized with ease, However, as them rocks are not tr ~iblesource of petroleum, they mere not examined in detail and will not be described at length. The volcsnic rocks were stt~didby Martin and &tz6 and were described in their report. They form a thick series of volcanic beds that include both flows and tuffs and are characterized especinlly by arnygdaloidal basal and volcanic agglomerate. Martin found " fine-grain4 green and gray felsitic rocks and tuEs, in partl cherky, invaded by large dikes of quaitz-feldspar porpllyries" on the north shore of Iiiumna Bay. Basalt, gahbro, and tuff are present on the west side and head of Iniskin Bay and olivine basalt, tuff, and an- desite on the head of Chinitna Bay. These rocks form a complex =mMage whose relations can te learned only by detailed study. They are separeted from the Jurassic sediments of the west shore -. - .'Wrtin. 0. c., and Kae. F. 3.. A WaeolMc lpconnaisaance of the Iliamna reHon, blnskn: W. 8. Ocol. Sumq Bull. 483, g~.W9, 1912. of Cook Inlet by a profound fanlt or zone of faulting mmy miles in length. Martin found that the voImnic roch on the wuth shore of Cotton- wmd Bay, at the head of Ilimnm Bay, rest apparently in conformable stratigraphic succession on the Grnishak chert ( Upper Triassic), a relation which would indicate that they belong either high in the Triassic or low in the Jurassic. Their relation to the Kamishak chert and their lithologic resemblance to rocks in Seldovia Bay which have the same relations and which are tentatively referred by Stanton h the hwer Jurassic led M&in to assign the volcanic rocks of Iliamnn Bay tentatively to the hwer Jurassic. The volcanic flowa and tuffs of Iniskin and Chinitna bay^ are part of the same belt of rocks as those at Cottonwoad Bay and are accordingly regarded as of the same age. Other localities where similar rocks of possibly the meage have hnfound are given in the correlation table opposite p%ge22.

TUgkbllZ BAwDmOBs Ghmactw md d&trib&ion.-The Tuxedni sandstone is not a homogeneous sandstone formation. It consists pri~cipa1Iyof smdstone and sandy shale, but includes also conglomerate, grit, ark=, and, in the type locality, limestone. In general, the lower pert of the formation shows all the mks rnenhned, but the upper part ia made up of sandy shale with which thin Wsof sandstone in subordinate amount and rare conglomerate beds are interstratified. A generalized &im based on observations of the formation in different parts of the district follows:

Shale d nahmwn thickma Feet Coarse sand&ne------,,------+-----+------, T5 Shale-,,,,------1,000 Coam conglomerat~.

Shale ---,,,,,,,,--,,,,,- ,,,I 800. Gray sandstone. SbaJe ----r----d------+,,-,,,,,,,,,,-,,,--,,1, Conglomerate, - marae ,,,-,,,,----,------20 Tbln #hale band. ITcnvy andm me bed. Dnrk shale--,---,,,,------,,------,---- 1,200 Fin~-grainedmy aandatoae with smaU hcdn of shale and andy ahde------d------,------*------1,W

Con~lomernte------,,,,,,,--,,,I ---- -I 30 Sandy bedq fnclnding sand8tone. mndy shale, and cm glomerate,,,,,------,------,-,,------++-~---,- X3ctrL shale, andy shale, and tbtn andstme------,,,, This formation is emdong nearly the whole muth shore of Chhitna Bay and the east shore of Iniskin Bay and accupim ap- pmakately -the northwestern half of the peninsula, including the :vallqw of Bowaer, Fitz, md Park Creeks and the upper vrrlleys of Bmwn, and Bow Creeks. In gmeral the topography of the area shows smooth slopes with rounded hilltops and broad valleys. The part of the peni&lra west of Fitz and BOWS=C& is believed to be occupied chiefly by the lower part.of the Tux& sediments, in which'hard beds of sanddone md conglomerate are numerous and through difFerentia2 weathering have formed many waterfalls on smaI1.atrmms that drain the ridges. A more detailed section on the east shore of Iniskin Bay, which includes 0nly.a small part of the whale Tuxedni formation, was maasumd by Martin' and Stanton and is given to &ow the vari- lrbility of the beds. Such variability is mom characteristic of the

, lower 'pad of the formation than of the upper part.

8e~timof Tuxedmi mndatom on east #@re of Ininltfu Bay, Araah kc met PJanm ahale Pritb maw Belemnitea and otb@rfosslla-,,,,,,, M) : Oo~Ie4-,,-,------e4e4----e4e4e4e4e4---e4e4,e4e4-20 Soft shal&,~~,,------__,------~~------20 Dark-drab shale wfth scattered fmils,,---,,,,,,-- - 33 Hard calmrmna shale full of fosdls. principally I~~rnua, PImtrrornya, and other pelecmds,,,---,,,,----,-,------, 2 Black mdatone~-----,,,,------~--~---,~,----~1 Dark 8haL-,-,,----,--,--_------~---~~------~~~K Blnelr ands stone--,---,,-_------^^---^-^,, 1 . DarkshaEe,andp3anyfosrtHa-- ---,-,,,-,------,-,12 4,,, aeddhb limestone ,,,-. -----,,------,,,,---,------,------$

Dark &ale with many fornil8------,,--d,,,,,------14 Dark shale with scattered iowilrr ,,,,--,,,------62 Dark mft Band~tonewith ~t~eak~lof c~ll~lomemte-,----_,_ 10 Goncmled. hmB mewith weral fmsll bands rontafalna Trigonfa doro- acMd and other imdls------,*------+------60 Concealed. ZDw A Wale wlth several abunde~tlriosslliferons beds each 10 to 25 kh~thick; Trfqnrtin dotonckisll, T. dcvem, and other iww---,------.------,w Concealed. Bbale ------,,,,------12 Coarse Eon~merate------,------L------2U Unconformity (?I.

nYartln, C1. C., and As*. F. J., 4 gmlo~Icrecanmi- of the nEam~a-on illanha: U. 8. Oenl, Buwey l~ull.485. p. 61. 1912. An unmnformity at the base of this section was thou~htto have been observed by Martin, but a further study of the rocks about Right Arm indie that the Tuxedni sandstone md the volmnic rocks on the wast are in contact along a great fault rather than rr plane ;of sedimentation. The exact position of this small section within the general aection is not known, although it appears to be in the Iower part, where alternations and variations of beds such as

nppr here we especially cemmon. 'm Th~chw88ad stmeEF1rn4tudy of the Tudai ssndstone during the summer of 1921 shows that the formation is much thicker than earlier work in Cook Inlet seemed to indicate. No single section * is hown where the thicknm of- all the beds an be memud eon- sececutively. The evidence of the thicknes is therefore obtained from ti number of incomplete sections in different localities and is subject to errors arising from the pmibiity of incomt correlation of beds in these sections grid also to possible duplication of beds arising through faulting or folding. Furthermore, the base of the Tuxedni ?andstone has never been unmistakably mmpized in this district, although the top, which wes determined solely on paleontologic evidence, was seen in a few places. The combined &ions from all the localities indicate a minimum thichess of 7,000 feet, more or less, for the formation. This total is larp and reprewnts a thicknew much greater than the sandstone is hama to lstbin elwwhere in Cook lnlet, so that some doubt is felt as lo its correctnem, although it is comparable with the thickness of the overlying Vpper Jurassic rocks in the Alask~Peninsula. The structura of the Tuxedni sand- stane is shown on the map (pi. 2) and is of particular significance to these inter&& in the problem of finding petroleum in the district, for the known seepaps and the holes that were drilled and produced oil or gas are within the area of this formation. The valley of Portage Creek, which extends northeastward from Right Arm of Ini&n Bay to Chinitna Bmy, marks the course; of a pat fault and the axis of a clowly compreswd anticlinal fold which meet ach other at a slight afigle. AH the rocks on the west side of the valley, except a small rrrea on Ri&t Arm, belong in the belt of volcanic rocks that borders the mein mountain range. The great fault that brought the Tuxedni mndstone into contact with the volcanic rocks appeaM to lie on the west side of the anticlinal axis at Right Arm but cro= to the east side in the valley farther nort;h, for it cuts off 'the west limb of the anticline. The valleys of Bowser and Fib Creek mark the position of a md anticlinal fold, parallel to the fold previousl_~ddbed snd somewhat less cornpremed, which &ends hmthe vicinity of the, head of Oil Bay to Chinitna Bay. This fold is commund snd divides .I. VII;~~1'1' I\ISKI\ T{.\Y Y~II~I,4 I'III~'~ ?.j,;.ilt 'l.11~!<\I) OF 'I'I~IIL xi \(;(IS r{o,\rJ'1'1) 1111, IJ.AI

Slw~r.iIlr~t-lyi~~t: l*.tIy r,T T~uerllli~lnlldrtonc

5. \ lE\\' TO 'I'll K SOL.l'tt ;\ND US'l' ACROSS TTE Ejl 3 FLATS AT THE lIH.\I\ 01.' 1'1.11 NI'I'NA Il,\Y Slroas t.hrrrlnel rolloawl Ily strennl md tide ruld ddvr-ro~rrcdh1uj~a.c ur~ n~n~tutni~tu ~,T.I'uxn:el~~i 'ir~1r~l*11~1*.

inta two minor anticlines in the Fitz Creek Valley. East of Bowser and Fitz Creeks the Tuxedni sandstone dips toward the coast and pmbsnegth the Chinitna shale in a manocline which is inter- rupted in places by small local folds. The western anticline is hidden on the buth by the waters of Right Arm and Inisgin Bay, so that nothing is known of it there. but the anticline of Bowser and Fitz Creeks, together with the synclinal trough between it and the Right Arm anticline, flattens out towad the south and pitches or dips beneath the younger rocks of the mounhins between Iniskin and Oil Bays, The relation of the Tuxedni adstone to the Chiiitna shale between Iniskin and Oil Bays is not simple, however, for faulting disturbs the normal relation, as is known from the exposures on Iniskin Bay and the absence of the higher Beds of the Tuxedni sandstone. Unfortunately, the low hills formed of the shale between Oil and Iniskin Bays am so thickly capered with timber and particularly with alders that only scanty information about the faulting was obtained, in spite of the realization that such information may be important in con- sidering the accumulation of oil. Age ad cm&ion.-The Tuxedni sandstone is the most highly fossilifemus formation in the district and contains abundmt fads at many horizons. Numerous collections were accordingly made to assist in determining the position of the boundaries of the formation and to supplement the collections of earlier workem, yet the number of species found could unrloubted1y have been increamd if more time had been available. On the evidence of the fossils ml- l&ed in former pears the Tuxedni sandstone was determined to be of Middle Jurassic age. This determin8tion is further corrob- orated by the collections of rnarin~.invertebrate fossils made in 1921. which were submitted to T. W. Stanton for identification and are 1kt.d below as described by him. IU[YiO. F 2*'Swtli short! of Clifnitna Buy. Mmt: easterly exposure of Tux- e8nl on west side of Fits Creek beafllng agaht Rowser Creelc: Pecten sp. Smooth ftrrm. &%milnot dIBtincti~e. SiKW. F 3. SontZl shore of Cblnitna Bay, 800 fmt mtof locality F 2: Btepheoeeras carlottense (Whiteaves) ? Probably horn the Taxedni sandatone. 1M. F 4. East dde of Fltz Creek, 3 mfl- mth of muth shore of Ghinltna flay: . S~haermrasoblatum [Whiteaves) ? ' Phyllocems sp. Snxednl aandstone. 1OgSa. F 6. Head of Bowser Creek, south aide of valley at about elmtlon so0 feet. Xnoceramna ambiguus Eicbwald. Flenromga tsp. Tnxedni sandstone. 11OSg. AB F 47. 2,000 feet farther up creek tlyn AB F 48: Ternbratala m. 3thynchoaella sp Cnmptonwtes sp. I'ecten ap. Smooth form. Pterlrla asp. Larw, strongly mlptured. Pterta? q~. Trlmnla ~tp. Astarte ~p.Two nr more apelea. Phyllmra~np. Tuxedni sandstone. 11040. AB F 40, 1,120 feet from dB F 47 on flmt right fork of lett fork: PectPn RP. Small ribM form. Pecten sp. Smooth form. Inoceramna ambigunq Elichwald. Grammatodon up. Plenromya sp. Undetermined galstr~pod. Belemltea m. Turedni sandstone. 11041. AB F 50. Over hill from Iom11e MI F 49, ta next creek to went at elevation 800 fmt: Inoceramys %p. Grammatodon PII. A~tarteq~. Cadocems domhinl (Eichmld ) . Cndocema stendoboide Pompeckj. 8phhtreroceras? ap. R~1~mniteasp. The pelwmds in this lot suggest theTnmdni ianna, but the ammoniten certainly came from the Chinitna shale. 11042. AR F 51. On tributary to 5owser Creek from mtb, about 1,900 feet up creek from trdl mslng. ILmten AD. Lima up. Pt~rla?RP. Eumlcrotin? sp. Grammetodon sp. Grammatodan? sp. CeritbIam sp. 8pbnermrn~sp. Relemnitea qi. Tnxwlnl nandstane. 110436. AR F 63, On same tribntar;r mmtioned ntmde~ dB F 55 ahoDt 2,lVM fmt up creek from trail croe~slng: PhgUoceras 8p. Fossil not 81Eltlnctiv~. llW4a AR F 63. 5,800 feet up creek from trail crdgat elevation 800 feet: up enst fork at 2,m feet: Trigonla sp. Fr~meatargimpr5nt F&D not distlnrbive. UW-AB F 34. 3,900 feet up creek ddklunder &B F 61 nnd up -st fork at !2,SQO feet, at elevetion SBO feet: Aarte pp. . Probably 7hmdd mndstane. 11WB. AB F 66.4,400 feet up game creek mendone8 mder 833 F 51 : Inoceramw mbigons Eichwald. Tuxedni sandstone. UQ47. AE F L%8.,800 feet up same mkmentioned under AB F 61: Terebtatula m.

Plenmmya sp. Xntica sp. nlacrmphalltes g. Phylloceras sp. OPpeIla? zsp. Belemnitea ~p. Ttmednf eanhtone. 11W& +4R F 57. At tbe forks. 6-M feet up game creek mentioned under AB F 61 : Phyllocerns sp. Oggelia? tsp. Probably Tuxedni sand~tone. U061, AR F 62. &,400f~et lip wnth fork of creek mentlnned ander AB F m: Oamptontxtes sp. Inoceramas ambiguaa Eichaald. Macrocephalltes? ap. R~lemnltesm. Tuxedni sandstone. 1lW. An F U4. Chinitea ehale. -4 sbort distance above assumed Tr~xprlnl- OhInitna contact along mkmentioned mder AB P 51 : Tbmda? mp. Oppella? sp. The ammonite mggests the Tunedni fanna rather than Qhhitna. nOh17. AB F 70. Bonthward along east shore of Inlsldn Bay about 2BO fet tmm end of tmfl it lower cam: Trigonia ap. Tnxedni sandstone. 11081. A15 1.' 77. Northward along east sbore of In!- Bag 5,400 feet from end of trail at lmrcabin : Pecten sp Pterla sp. mark? pp. Trigonfa ~p. Arctlca sp. Quenatedtin? m, Pleuromya sg, Wacla? sp. Anatina? sp. Tuxedaf mndt&me, but was given a distinctive name, "because of the dissimilarity of the lithologic character and f amaa of the two prt9." L4 The Tuxedni smdstone of the Inigkin-Chinitns Penhula is part of a belt of Middle Jumssic marine sediments exposed along Cmk Inlet from Tuxedni Bay to hiekin Bay. Its characteristic fauna has hen found in Matanash Valley IPand in the "rordrillo forma- t.ion '"around the headwaters of Skwentna River. The fauna was coIlected BISO by ,Moilit l4 and Chapin from a small area of tuffaceous sInte sssocisted with conglomerate near the mouth of Chitina River, in the Copper River basin. Capps collected fossils from bedded rocks, including shale, sandstone, and conglomerate, on Wide Ray, on the Alaska Peninsula, opposite the south end of Kodiak Island, which Stanton regards as of Middle Jurassic qp but somewhat older than the fauna of the Tnxedni sandstone in Cook Inlet, although the fsuna f& Wide Bay includes the lowest part of the Tuxedni fauna of Cook Inlet. In 1991. when Capps visited the area, not more than about 500 feet of Middle Juramic beds were mpized. More recent work by IV. R. Smithta however, has shown that the Tuxedni beds in this locality are at Iesst 1,21W) feet thick and that the upper 600 feet probably is equivalent to the Iower beds exposed nt Tuxedni Bay. Fur- thermore, a new locality southwest of Alinchak Bay waa dhvemd, - where about f,3W feet of Ms, chiefly sandstone, referred to the Tuxedni snndstone, is exposed. A section of bedded rock on the shore of Krtmishk Bay in the ricinity of Amakdedari is described by Mather17 as belonging to the Tuxedni sandstone. The rocks expod in the CMSat the mouth of Amakdedori Creek include about 500 feet of foss3Serous sedi. ments, comprising dark carbonaceous shale, gandstone, pit, and volcanic tuff, and are both overlain and underlain by dense basic lave flows. This section is themfore somewhat different from the others 3 just described. Sside from these three localities the Tuxedni sandstone has not been identified elsewhere on the Alaska Peninsula, although Upper Jurassic swliments are we11 developed. The Jurassic sedimentaq formations of Masks, so fsr as they are known. are shown in the following correlation table :

'JMartln, G. C.. and Kainrz, F. Z,, A gmlogfc reconnaiusmcs at the fllarnna reglrm, Manta : U. -1. Burvey Bnll. 486, p. 68, footmote 4,1812. Faige, RlUney, md Knopf, Adolph, Geologic reewaaiwmee in the Matmmauka arid Talkaetna basha, Alaska: U. £4. 1301. Rawcy Boll. 327. pp. IS-19, 3967. Rrooks. -4. H.,The Mount Mcfilnlep redon. hlash : U. B. Owl. Samw hoi. Pawr 70, to,. 90, 1911. 'MofRt, I?. H., Geology ot the Hanaglta-Bremntr r@m. blanks: U. 8. Oeol, Barney Bnll. 676. gg. 25-27. 1914. " Capprr, 8. R., The Cold EUy dim& Alm&m : W. 1. (3tol. Stmay BrrlI. T89, p. 82, 1022. I* Personal commanicetlon. 'TMother. K. F.. Mlneral mnm~at the Esmlshak Bay regon: U. I.-1. Elurw BUII. 773, p. rm.1925.

Inhive rocks in the Tuxedni sandstone are uncommon ; and the % only ones that were obssrved me confined to the hinity of In iskin n Bay, They include sills of quartz diorite and bamltic dikes. Two sills of quartz diorite, one of them 10 feet thick and the other 50 feet thick, were seen on the shores of the Right Arm of Iniskin By The rock is soft, dark greenish pay, and speckled or mottled with small blotches of ~lteredfeldspar but is so dens and fine gained that the other minerals can not be identified with the unaided eye. In the places where the rmk is exposed it is weathered and f~luch altered, so thrtt it is soft and breaks easily. The sills crop out on both &oms of the right arm snd are structurally canformrrble with the beds of sandstone and congIomerate with which they are associated. Under the microscope it is seen that the rock owes its preen color to chlorite. 1.SeveraI dikes that cut Tuxedni beds are exposed on the east shore of Iniskin Bay. They are not conspicuous, for the color of the weathered dikes is much like that of the including shale. The dikes are cornpwed of dense fine-pained bIacZr basalt and are less than 10 .&& in thicknes. At one locality a small dike, 10 inches thick, is amygdaloidal, the vesicles having been filled with a, white secondav ininsral resembling henlmdite, The microscope shows phenocrpts of feldspsr, augite, and olivine in a poundmass of feldapar and augite. Neither the sills nor the dikes are indicated by topographic features. No direct evidence of their nge was fodaside fcom the fact that they are manifestly younger than the MiddIe Jurassic rocks which they intn~d~.

The Upper Jurassic beds include, in ascending order, the Chinitna shale md the Naknek formation, the latter including the Chisik r - I eonglomerah member at its base. These fornations succeed each other snd the Tuxedni sandstone without structural unconf omity and form a belt of high mountains, averaging less than 4 miles in width, along the coast of hkInlet from Chinitna Bay to Iniskin f Bay. About llalf the area of sedimentary formations mnpperl on Plate 2 is occupied by Upper Jurassic rocks.

Chterand dbtrhtim.-The Chinitna shale consists of pap. black, and reddish argillaceous shale in which are interstt-atified in mme places sandy and calcareous beds and in a frw plsw beds of This formstion is of fairly homogeneous charmtar and differs from the prevailing shale of the upper part of the Tuxedni smdstone in that the older shale is arenaeons rather than argillaceous, yet it should be noted that the shales of both formations at their g contact are similar in appearance and cornpsition and nre didin- h guished from each other on palmntologic and not on lithologic evidence. Lines of fossiliferous concretions, indicating the bedding . plmss, are numero~isin the lower part of the Chinitna &ale. In most places where exposures are, good these fossiliferous mncretima make It possible to determine within narrow limits the boundary betmeen this and the underlying formation. The upper part of the Chinitna shale, on the other hand, yields few fossils, but is characterized, by discontinuous thin calesreous beds which are shapad like much elongated lenses and have a conspicuous yellowish color : where weathered. These yeUowish bands, although present throughout the upper 500 feet of the shale, give much amistancs in dekr- mining the position of the boundaq of the formation. The Chinitn-a shale occupies the intermediate slopes of the Isnd- ward side of the coast mountsins, overlying the Tuxedni sandstone of the foothills and lower slopes and underlying the Chigik eong1am- erate and other beds of the Naknek formation, which form the brow and crest of the ridge. It thus appears on the nap as a narrow band, nowhere more tllan a mile wide. The type section of the Chinitna shale on th0 north side of Chinitna Bay, as measured by Stanton,'@is as follows:

#&dm of OMni#n@smls on n&h slbwa af U&hiirc~Bay Feet Indnrnted dark am1aceous &ales dth conapimons thin haads md donfgtted knees of yellowl& impure Urnmime, BOO At Ehls point a change in the strike of tbe Ma and Lo tbe drection of the coast rmrrles the cliUa medistance from the ehore. The sertlon la continuerl on a mall me8 that enkern the bay about half a mlle west of the end of the area clMs. Along tbIs creek the expomum are not rn contlnuons nor BO consplcuons aa tboae In the sen as, but they are sufltient to fibom the relatlon of the beds to the finera1 8ectIon. Dark shrtle~which In places cam more indurated tmnds of aFgf1lnmns rrendstone ,,,---,---,,--,-,,,-,,,,,---,,426 Dark shales and beds d a~~ sandstone, forming many cascades; Cadcreemr iuund near the middle,,-----, 8M Indurated bands of arglllaceons mndatone: abundant specl- mens of Cadocmas and Belemnitw ------,,,,,,,,,,,10 Dark &ah and erfflllacwufi sandstones------,,------115

UBtanton, T. W., and Yarttn, Q. C., Meao#oic nectlw of Cook Xnlet and A1amh Peni~wla:QmI. Soc. dmerfca BolL, wl. 18, p. 400, 1005. Feet Bimtlar beds not well ex------,------200 Dark shales which in weathew form btownbh slopes dth bands of small concretions containing Cadocemr dore mUnC and other fossil8---,------+------711 Dark clay ahalea, weathering brownlab. wit11 M~crettOIIb containing Cadoeeratr and other Zossil~near middle------110 %W The &ions on the east shore of Iniskin Bay and Oil Bny are ahgiven as measured by Stanton and Martin, for although they were revisited they were not remeasured. The section on the shore 1 of Iniskin Bay begins at the fault contact of the Tnxedni sandstone and Chinitna shale, about 1,000 feet south of the trail to Oil Bay, and extends southwestward 7,000 feet to the outcrop of the Chisik conglomerate, including 1,308 feet of beds as shown in the first sec- . tion below. The base of the shale is therefore not mprnnted in the

8&h or OhfiJtm shds on eadt ahom of I~frkbBay

~tvkkrabshale oontaining nnmerana bands d limesrtooe mncretlone Wed with well-preeerped emof C&wemaf BeEemwUes, and other foaslla, and alm a few &ich ot fo&lIzed wood ,------,,,,,,------*--- Shale as above, partly concealed by talus at "Maehnwm Wka" : thickness computed-,,,,,,-,,------Dark abates, as above, containlug nme mncretlom and arood----*,,--,-,-,,,*,------*------

Limesto~e------I------Shales, = abve,**,**,,*------,,,,,------8hale1, mrtly mded by talus; thiclcaess mmpntad,,,, Shales, m above, contatning Cadmxms dwhMand a few ather fosslls--,,,,--,,-,,------*------Con~--,---l------1------r-----r-

The &ion on Oil Bay is as foHows:

Bedfan of upper part of Ckhltrto ahole on east of OU Bug

Fet Dark ahale wltb concretlona ,,,-,,-,------65D

Hard dark windstone-,,,---,,,,-,------%-Ti Dark-drab &ale with numerous concretions----,------530 Calcaraoua shale wfth Cu~~awhmMtI PomWj, Cadoceras sp. ci. C. at.mlolMe Pommkj, aad Phytb ceree,,,,,,,,,,---,,,,,,,,------,------I Dark shale with Cadowron dwoschid and other fossilt~,-- 80 Wft green sandat~ne,--,,,,,-,----~~~~~-~-~~~~~~~-~1h Dnrk-drab hale-----^-^-,,--^^------*----- I2 1, This -tion slm begins st n point somewhere above the base of the @hale,for the top of the Taxedni sandstone is not expml at this Id*. Thkkmaa ade&M.-Tbe thiclm- of the Chinitna &ale in . its type laculi6y as measured by Stanton (we p. 24) is 2,086 feet, and that of the partial aections on Iniskin and Oil Bap is 1,308 and 1?94 feet, respectively. The base of the shale is not included in sections on Iniskin and Oil Bays, yet the thickness repmyented by them is nearer t the thickness of some other sections between Ini&n and Cbinitnn Bays than that of the type ~ection. A mtion st the head of Bowwr Creek gives 1,400 feet as the thickness of the Chinitna shale. So far - as is known this thickness is not msde questionable by folding and ftrdthg, although faults might be difficult to detect. Such a thick- nRss would contrast strongly with that of the type section. Espe- cially does it contgst with the Shelihf formation on the Alaska Peninsula, which reaches a maximum thihem of 7,060 feet and cw- ries the chinitna fauna, although it has not besn correlated with the Chinitria shale. The Chinitns shale nearly everywhere haa a seaward dip, although at one locality n amall fold with revem dips wae BBBL In general, then, the formation has a rnonoclind structure, with dipa that range from 15" to a maximum of 3s0 (pl. 6, B) and strikm thnt approxi- mate the trend of the coa& line. Age and cmIatim.--The. Chinitna shale was at first included by Martin in the " Enochkin formation" and mgarded as af Middla Jurassic age. Later stndias, however, Id to its separation from the " Enochkin formation " and assignment to the Upper Jurassic. This formation is lesa fmiliferous than the Tuxedni sandstone but pidds numerous fmils at some horizons in its lower part, especially certain smmanitea, among which seveml species of Cdocerae are. prominent. Theee forms were regarded m diagnostic in mapping the formation boundary. A list of marine invertebmta fomils from the Iniskin-Chinitna Peninda, identified by T. W. Stanton, follows: 10978. F 1. South nidc entrance to Chhdha Bay; 100 feet-west d pint 2% milea emof Camp Point : Cadocerna ~enolobofde!Pommkj? Chlnitna ahale. 10982. F 45. Head of Bowi#* Creek, month dde of valky at levatEon of about 1,000 feet above sea : Carlocerm doroschlnl (Elleh~d]. Cadateras? sp. Globe form dth verg narrow umblllemr. - Chtnltna shale. 1OOMl. F R. Tributary to Bowser Cr#k frnm muth, next blow head branch of stream ; tbree-fourtlm mile below forka of stream at 10~lllity507: Oadoceraa sp. Chlnitna sbale. F 11. shore of Inbkh Bay, math of trail to W Bag: MlweBp. (ladmrae doroscbini Elchwald. Chinitna We. lW@O, East ~hmof I&Bin Bay, 1 11e mnth of trail to On Bay: Caderas stenolobolde PompeckJ . Chinltna ahale.

c 10991. Baat &ore of Ini@kIn Bay. I mIle sooth of trail Lo Oll Bay. Float : Haqweraal mp. Cosmoceraa? ~p Probably Chinib shale. 1m2. F 14. Elurt shore of Infakin Bay, I mile south of Trail to OU Bay : Kepplerites? sp. Verg clowly relaterl and pow1Mg identical with Am- rnonlka logambnm Whiteaves. Chfnitna male. 1- AB F 1. South ~hored Chinitna Bay, In npger member of Chfnftna ~hle: Lncha? sp. Fwd not dlktlnctive. 50986. AB F 3. South shore of Chlnlha Bq, In nmr member of Chinltnn a1e: Inoceramus BP. Pleummga sp I Foaalls not: didnctive. lW7. AB F 4. Baath shore of Cbinllna Bay, in top member of ChinitDa ahale : Phyll~sp. Claw of a rraatecean. Fomtls not d1Ftinctive. 11OIJtL kR F 10. South shore of Cbinitna Bny, fa top membw of ChiJtna ahare : ~ad&ras dorawhini (Eicbwnld) ? Chinltna Ahale. UW AB F 12. South ~homof Chlnim Bay, lo talas probably from be& near top of Chlnltna sbnle : Pecten ap Smooth t fom Fmdh not dlatinctl~e. 11#XK. AJ~F 35. &utb more of ChWtna Bay, in talus, probably fmm Ma near top of ChInitntna Rhale: Rbynchonella SF. Aatarte sp. Tellina? sp. Fosslls not dlsltlnctlve. 11008. XB F 16. Uo~~th~hore of Cbinltna Bmy in unpper past of Chhitn~ &ale : Qrammntodon sp ' Fn~silsnot distinctive. llM6. AX! F 18. South dore of Chinitna Bay, In upper middle' part of Qblnitnn shale : Fragmentary tmprlat of an undetermined gaatrw with pomIb1~h- crusti ug br,~omns. 11M1. ,4R F lo. 8onth shore of Chinttna Bay, in umr gart of Chfnltaa shale : Pbyllwemir sp. Pdl lint dlstinettve. . 11012. AB F 20. Bonth shore of Chlnitna Bay, from nwr paxt of i=btnitna shale : Gmmmatdon m. Leda? RP. Small venwld? Thrnda ~p. Burrows of n pelecBpod? Ihsslls not dhtlncttve. llWD. AB F 58. On tributary to Bowser Creek from moth, 8,080 feet no I-reek from trail emlng: Cadmadomhlni (EEchwaId). Macrocephalitm sp. C=hlnitna ahale. 1 llOM). 4B F 59; and 60. 0,400 feet dp creelr leadLng to peak east of C T peak : Cadocems dormhlnl (Eichwald). Phyrloceraa sp. Chiniton shale. 11052. dB F 63. About 9,000 fez$ up ek: Ctlrlm-eraa dorascbini (Eichwald). Chinilma hale. 11m2a. AH F 88. J%Bt shore of Oil Bay at northad comer: Cadocens stenoloboide (Pompeckj } ? Chinttna shale. 11063. dB F 64. A ~hortdiatnnce abo~eamurn& Tnxedni-Chinitna contact dong abovementiweti meek : Thracia? sp. Oppelia? sp. Chiniha ahale. The ammonite saggests tbe 'lbxednf fauna rather than the Chinitan. 11W. A3 F 85. About 613I tet down west shore of Oil Bay from Bowser Cmk : Peeten 8p. Pterh sp. Qmmmatodon ap. Amberleya 8p. I Belemnltee E@ F Fosaila not dlstinctlve. IllMl. AB F 76. Just below contact of C'hinlbm dth ChIaik beds on east shore of Iniskln Har, &20fl feet down abme from trail to 011 Ray, about 75U feet Mow Toadstool T~lands: C Flenromya sp Thracla ap. Cadoreras grewlngkl Pompeckj ? CbInitns shale. The following lists show the invertebratk and plmt fossils col. lected by Stanton and Martin on Chinitma, hiskin, and Oil ~a~s and include a number of species not mentioned in the foregoing list. The plant forms were identified by F. H. Knowlton. 3018. CbLnitoa Bay. Upper part of Cudbcwm me: Uacloceras sp ; romp- r%bMform. Cadoceras dora&M Eichnald? Belemnltea m9. Chlnlha Bag. 8everal han&ed feet lmr than 3M8: Cadocerna doroacbinl Elichwald. Cladoceraa sp.; lw convex form. Cadocerm ? ? ; smooth clomcolled form ; nmbllim mrlp el& m. Chinitna Bay. hwer than Sole: Cadocem domschhl l!Nebwald 7 Ckxynotlceraa 7 ; smooth sharp centered form. BeJemnlt~; very large phragmamne.

T iao22 Chidha Bay at w& end of clIEa north d camp: Plearomya Ooniomsa APicala. Undetermined gadmmia: verg mall. 8028. EuochB1n Bag. Onecfonrth of a mile below lowmMn, 0- zone: Cadoceras doroeehLni (Eichwfild). Cadoceraa ap. Cadoceraa 8~. Cadoceraa 7 Spbaeroeeraa P4p1Iocems. Oxynoticeraa ? Ceri thl urn. Grammatodon. Avicnla. Pacten md othes f'o~mrr. e.Elnochkin Bay 1 mlle below Powsr abln. 0- me Oadoceras Bom~~hioi( Eichwald ) . Oadwe~asap. cndmms 8p. sphacroeeraa. PhyUmraB. Oxynotieeras? Belemnites. orammatodon. Peeten. Thracia Gontomga. Pholadomya. detarte. Modielaf m. EnMnBay 1% d1aMow lower cabin : Cadoceras doroschLnI (Eichwald) t Cadoceraa ep. BelemnItBB ; very large pbragmamne. W. Oil Bas above Gadmas zone. Neat Inrge waterfall: Cardlmraa rrp; not in phw. Phyllocerm ;ap Pemen. Torbe. m. Of1 Bay. hmr M) feet of ~m.Oadmas mw. Cadmrm dom&lni I0ichwrrld. Qndocems 5p. Belemaites. Pleuromya, two sped@. P&en and other forme. 19565+27---3 No. m. Blast &ore of Id- my: ' Caaoceraa aloroeddni (~&ddS.. Abundant C~doceraawoanwwmkii (Grewingk) . Cadoceraa scbmidtf Pompeclrl. Cadoceraa ca toatoma Pompecuf

M~crocephnlltee'lsp. Fhsllmrm mbobtdforme PompxkjY Btephilnocem sp. Form &gum3 by Eimd as hm. astl~~* n'orblgay ait BeIemn Itea sp, a. One eea Goalorn~aep. One mall men. Lima RP. Fecten ap, 0maU emoath form Plenrom? ap. One fqedmen. Serpula? sp. 8mall dlscoidrtl form abundant in cme rock fragment. Several tlndstermlned blvalm reprwented by impede& material. No. 2941. last more of Oil Bay, 72% feet above base of -on : Cadomran schmidtl Pompeckji. CadOe~atlsp. cl. 0. $tw~lOb~idePornpeck$ Phyllocemn fip. rJo, 929. Inlmkin Bay, eaat shore, half a, mLle below lower cabin: Cl aclmhlebfe dlentlculnta (Brongniart) Nathorst, Ctenia gmndiiolfa Fontalne. Hauamnonfa ~p.? Mere fragment. DictyophpUmm Ci. D. obtnaIlobum. No. 929a. Intsb Bay, eaat shore, I miIe below Fosdl wood, not etudiea. Tha bp donof the Chinibm shde is the donmeasured by Stanton an the no& shore of Chinitna Bay. (See p. 24.) The shale, lhthe overlying Upper Jurassic beds, extends northward to Chiaik Jdand in Tuxedni Bay (em p. 66) bnt is not horn to be pmnt farther north on the west shore of Cook Met. Pdp and &opfle found a series of concretionary sandy shale and sandstow beds, to get he^ with same conglomerate at the head of Little Nelchina River, north of the headwaters of Matanuska River, from which they collected the Cd0cem-s fauna, at that time regarded as indicative of the upper third of the d( Enochkh forma- * tion " but now included in the Chiniha shale. The greatest known thickness of sediments mnkBining the Wtna fauna is on the Alaska Penin~uhnear Wide Bay. This mtion was diedby Capps,gOand the beds were given tbs name Shelikof formation The metion includes a thick series of mdstone, together with mme conglomerate, sandy shele, and calcareous shale, all overlain by black able containing Limestone Eenm near its top. mesa

Hld~ey, mud -mi, Molpb, Osoloqlc mmmnabmnee in the Ma- mad TrIlaetDauILubr:u* 8.43mL 13artl.W. 817,gp. !2&28,1807. mhpp.. I.B., The Cold Bal oil dimtrlet. hlash: 0. 8. OeoI, hmep Bun. T89, .B. 91. lox!. dimmts, prwailinglg ~dstone,mh a maximum thickma d 7,000 feet and have a wide distribution. amTO%YIzmm

:Q-~ar adsrrbdi&bw.-The Ndm& formation, lilLB the TUX- hdndm a heterogeneous mixture of shale, mmdstone, uhm, andeitic tuff, and conglomerate, and in the region between t Chinitne Bay and Oil Bay it may bs separated into 8 lower md an upper part with distinctive lithology and deciddy conspicuous dif- farenoes as expressed in tnpography and the lands~@pe,These two divisions continue wadward from Oil Bay to Iniskin Bay, but about I midway between these two bays a coarae massive conglomerate 290 feet thick, which is here mspped as Cbisik conglomerate member, occurs heath the lower division and extends westward to Iniskin Bay. AE the Chipik appears to be equivalent to the basal arkosic beds of the Nhek formation of the vicinity of Chinitna and Oil Bays, it is here treated as rr, member of the Raknek In the area between Chinitna and Iniskin Bays the lower pad of the formation, or the bds rnttpped as " shale and arbic wndatcmae " md ranging from about 1,500 to 1,646; f set In thickness, mn~istsprk- dominantly of grey shales tbat have dark arhsic beds and hecon- glomemte or grit at the base and thin sandstones and sandy Ma scatted through them. Ths sediments werlying them beds rrre white or Light-gray sendstones that contnin an abundance of igneous material-in part tnff, in part clsstic material derived largely from granite or granitdike &, and in part intruave sills. This upper part includes all the ~emainderof the fom~tionexposed in the district. CWcongfonwrate 4m.-The --Theisik conglomemta is typically a mnm, massive conglomerate made up of cobbles and boulders of granih or diorite and other igneous roeb in an mdesitic tuff- mou~pun- The only locality within the area mapped where it is found with the chmscEer described is on the east shore of Tniskin Bay and in the adjacent momtnin. In this locality, as memad by Martin, it reaches a thickness of 290 feet. It Eiw with strpcturnt conformity on the ChinEtna shale luld is o~erIainin the asme way by the coam sandy beds of the Naknek formation. On the geologic map {pl. 2 $ the Chisik cong10fnerata i~ repmntad as a narrow band extending on1 y part way between Iniakip and Oil Bays, for tha beds immediately overlying the Chinitna shale on both sidw of Oil Bay are made up of grit or heconglomersta and arko- eic mdatone and bear no IithoIogic resemblance to the beds oceapy- ing this position on Iniskin Bay. In dl other places from Oil Bay to Chinitna Bay where the bme of the Nhek formation was examined the beds overlying the Chinitna consist of mame ark- ~nd hegrit Tha Chisik mq1omeFate of Inierkia Bay themfore sppems to be probably s IwaE phw of the ha1park of the Maknslr, and it is so treated in this report. It is mapped geparately bemuse of its distinct lithologic chamtar and its conspicuous outcrops, ralthougb B somewhat similar conglomerate of 1- thicknw within the Tuxedni sandstone was not separately mapped Blocks of the conglomerate have fallen f mrn the cli fls on the east shore of Iniskin Bay d have been worn by the sera waves into the peculiar shapeg that have given thean the name Mushroom Rocks, n name dm applied ta dsmall idan& near the sntranca to the bay. The type locality of the Chisik conglomerate ia on Chisik Ialnnd in Tuxedni Bay (see p. 671, where the beds resemble LithologicaUy the conglomerate of Iniskin Bay and probably have a slightly greater thkhe~6. 'me extent of the conglomerate at Tux& Bay is ah mrnewhat grater than at Iniskin Bay, nlthwgh st Tuxdni Bay also it seems to be of 1-1 development. Paige and Gopf report a similar conglomeFBte st htthe same stratigraphic position in the upper Matanuaka Valley. Chapin zs ddbeda similar conglomerate at the bsae of his Upper a as sic =tion on Nelcbina River ~ndmmlated it with the Cbisik conglomerate. At that time the Cbitne shale was still comidered to be the highest of the Middle JuFassic sediments. In the Cold Bay district, on the Alaska Peninsula, Capps found s massire bodderp clonglomerate at the base of the #&ek form* tioa, orer1ying nnh with the Chinitna &ale fauna md ranging in thickness from 'l0 to 1,000 feet and po;ssibly much more, Thin can- glomerate was originally included in the mica1 Naknek f omsfion of Spurr and is mapped as Nhek by Cappa Thua the beea of the dhentary formations carrying the Naknek fauna appears to be chanrcterized in the regions of Cook Inlet and tbe AlkPenin- srrla by elastic beds containing much material of igneous origin, in part valcanic, which ere nearly everywhere mnmr than the imme didpunderlying W, and in many pltacag are axmedingly mama and massive. Furthemore, &em beds ma not hown to fie, naar s Btructurd unc~nformity,such as might be expected in view of their wide distribution and the cotwiwneps of the materid mmpmhg them. Lithology.-Tbe upper md Eower pa* of the Nhek formation w m distinet in lithologic chsracter, and especially in their appearance in the landwepe aa seen in the field, that it haa -& desirable

amgldw, md -PC, Addbb, C)co~~ranmnei.pnce in he Ma-& am& 'PallttKtns barha, Aluka: U. & Oml. BumBult SZT, pp PI-!#, i8W. 'Chapin, Thdm The Nslchlna-BuaItnn redon, Alanka: D. 8. -1. 8urmy Bun. 0aS, pp. i36-SB. 1819. *Cappa, & EE, The Oold Bq oil .dlstrlct: U. 8. Oeol Bnrvm Ball. TSS. p. lQI,lOIP. to dkbgnish them mparateIy on the geologic map. The ~paratim is made on the basis of litho10gic character and not on the evidence of fossils. Them rocks are codbed to a curving belt ranging from 2 M 4 mile9 in width, which extends dung the whole seaward side of the pblsfrom hiskin Bay to Chinitna Bay. The bad arbsic Ixds are made up of material from a land mas where panib or granite rocks supplied an abundance of rock waste P for the formation of new diments and are believed to be the time quivalmt of the Chisik conglomerate of Iniskin Bay, for no conglomerate comparable to the Chisik conglomerate of Iniskin Bay was men district. of (i elsewhere in the The thicknas these coarse- grained basal beds is 147 feet on the e& shore of Oil Bay and is ~6ppmximatelythe same in other places where the beds were examined. Sandy shale with beds of sandstone succeeds the basal beds and tugether with them makes up the lower part of the Ndmek formation below the light-colored cliff-forming be&. This part of the Uabnek reaches a thickness of 1,845 feet in the sgction measured by Martin at Oil Bay. (See g. 88.) The remaining upper part of the Nbek formation is wnspimous (pk5, R, 6, A, and 8, A) wherever it crops out becam of its Bght color and because it re9ish erasion better than the underlying beds. It forms the dip slope on the seaward face of the mountains dong the cost, Its scarp makes the white cliffs along m& of the crest of the momhins, as seen from the landward side. This part of the Nalonek formation reaches a thicluies of possibly 3,000 feek The beds are prevailingly hard and massive bat in large exposum show distinctly the bedding lines. They include hard arkosic mndetone, sndesitic tuff, coarse and hesandstone, shale, and conglomerate, Thin silh of quartz diorite are intruded into the sedimentary bds * and me distinguished from them only on dose mination. The strike of beds of the Naknek formation ranges from about M. 30" E. on Chinitna Bay to nearly east on Iniskin Bay. The dips lare everywhere toward the sea and decrease between Chinit& and A Iniskin Bays from an a~eramof about 35" on CBitna Bay Ipl. 4, B) to abut 15" on the Iniskin shore. Loml variations of dip are found, as at Mount Chinitna, where the beds are tilted to an angle of nearly PB8, but no mch high dips were seen in the Naknek formation farther south. A better idea of the compIexity of the Nbek formation may be had from ak study of the detailed wtiom measured by Martin ~4 on

"Mirth, Q. C., and Kata, F. J., A geddc reconnaimmce of the Ilfilmlaa ram, Ahelm: U. 8. Qeol. Snrvey Bull. 485, pp. -72, 1912. the north shore of Wh Bay, on the east side of Oil Bay* and on fniPikin Bay. Theee sections am t~ follows:

Fmt CToan# mngimemte Wth granite wbblea 8 lnchm of hw In diameter and WIer pebble^ of variow lithologic Ehar- acter, In a Waceons or arkosiC XMMX--,, ,-,-- ,,,, 10

Conglmerate,,,-,--,~-,-,,,,--,,,,-,,,,,-,, % Mwiw t~~ rock with numerous tnclmiam,--,, B TaEaceona rock dtb much Bhnle,,,,,,-,,,,,,,,,-,,, S ana~iucflow or tm ,,,,,,,,,,,,,,~,,,,,,,,-,,,,,, 8bale---,--,----,,,,,,---,,---,,I,,,,-,,,L,,,, 2 Concealed~-,~-,-,~~~~~,~,~~~-~~~~~~~,,,,~,~~10 Andeedtic flow or tW,,,,-,,-----,---,,-, ,,,, ,- 16 Concealed~~,~--,~~,~,,~~~,,~~~~,,~,,,,,,,,,~~,~,~U Contorted shale with large RebmMbs 6% -,-- 29 SSaa-tone---,-----,,---,,,---,,,,,-,,,, ' 54 BhaPe ---d------,--,-----p 2,,,- ?h AndedtIc hw or hE-----,,, 4% Contorted mle with c~tion~,-, -- 8 Arkose with granite pebbles at to&,, ,-----7 Bandy 8Wle-~~---~-~~~~-~~~,,,,,~ 2 Bandy shale wlLb fwll brusd at top (Ay(pe1~~bed), 8 Dark abale --,--,,,,,,,,,,,,,,,, - 16 Conglomerate with &aly ma- ,,,-,,,,,,, 5 Bandstone---,, -,------c-- M

ConglomeratL,-,,,--,-,--,,-,-d-- 3 Dark shale,,,,-,,,,,,,--,,,,-,,,,,,-,,,-, '4 Con~lometateMth much sbaly mwr--,,,,,,,,,-,----, 13 A~fiEornerate---,,,----,---,------,,,-,,,--,,,-- Dark hale--^^,^^--^^^^--,^^^^^^^---^^,-^^,-^ 20 Cosri~conglomerate -,,-,,--,,,,,,,,, ,,-d-----,- 2 Plnldsh wdatone with bmds of pebbles,--,,,----,-,--, %

Dark shah--,,-----,,,,------,-----=--,,,--, Concealed (for 1,360 feet at 20. dig) ,,,,,,,---,- hdeaitic Pow or tuE,,,,--,,-- --,,,,---,,------ConmleB (for 100 fmt at 20' dip),, ,,,,,,,-,-, mealtic flow or tuE -,,-,,,,,,,-,,,--- Qonmale8 (Iw 6Q feet at 24)" dip),,,,,-, -,, bndmitlc flow or tatx-,, ,,,,,,,,,-,,,,,--,--- Concealed (Iw l3U feet at 20' dl~)------Feet bndmttic flow or W-,,,,-,--,-,,-,------,----,--- 32 aSplomeratete,,,--,--,,,,,,--,-~,-----~----- 3 Arkme with 0haly bmd~---,------,- 19 Anddtlc flow or tuff with agglomerate at he,,,,---,,, W .

Bhale-,,,-,,-,,-,------,,_ 6 ilndeel~cflowortu&,,-,,--,,,,,,------,, 79 Conmaled (for 420 feet at 28' dip) 182 dggl~mera~-,,,,~-,---,,-,-,,------~------, 63 dndedtic flow or tuff ------,---,,,-,--~~,----1M Shale---,,------,,------,,,,,--- 1 Bndesltic flow or tnf------18B ~lomerate-,,,--,-,-,,,,-,-,-,-----,,------,----,, 2 bnd4tIc tuft with ab~datpebbles ---- -, -----,------60 Bhale,,---,,-,,,,,----,,,----,,---,,-----,,-,,- 4

Concealed ifor 80 teet at 24' dip) ------I24 Bandy shal~,,--~,,,--,------'------,- 68 Bandstone and EihaIe------,d---,------,,-h-- 80 hddtIc flow or tuft ------,,--,,,,,---,------zs Concealed (across cove for 800 feet at 26' dip) -,,,-----,,SSS Goarss gray eandptone mostly heavy bedded-----,,,----,,, 66 dlternatlng bands of mndatone and &ale -----,,,,,,--,,,,7 coam grny 8anBstone-,,,,,,-,,------, J2 ConeeaIed,,,------,,---,,,,,,,---,,-,---, 10

hrse grny -Batone ,-----,------BB----BB---BBB 25 Bhaly sandstone_-,,----, ,----,---,,------,----,, 4 Coarge gray rra~datone,~------,~~------!M Coarw gray sandstone Mth bands of meconglomerate-,-, 5 Wsegray andstone wltb thinner'&aly bands !Z7 Coarse gray sandstone with badds of heconglomerate,,- 182 FanIt : dieplncement probably small. Coaree grey sandstone with baada af flne conglomerate,, 50 Dark ehaly aartdstone------,------25 Alternating ban& of shaly mianddone and flne conglomerate- 10 Coarse gmy @srtdmhaewith bands of me conglomerate,,,, 12 Dark shale 2

Oortrsm gray mdston~wtth fhe conglomerete--,-,,B--BB-- 21 Dark ahale with ReZe~raaaita 40 Coarse gray ~ndatone-----,,,------25 Dark hales with thLnner bands of mame gray mndstone--- 100 Wasdve coam gray sandstone,--,,------,--,---,-, 00 Ooame. gray sandatone alternathg with more shaly layem-- 126 Covered, except two or three small oatcrops of sand- stona-,~,,,,~,,,,~~-~,~~,,,~-~~,~,~-425 Dark slide with Bewe~,,,,-,,-----,,,, 160 ammbeI¶dd conme ~dato~,,,,,,,,, SO Dark sh611ea and san&tonm wrth BuaMa and other idls,,,-,,, ,,-,,-,,,,------m Alternafhg ot mnm gray and adlhcmua fodlitm- OPB 8snmn-- - 100 Qoaraegreynan-- 20 Feet TMn-bedded a%Ilaceoap handatone in lrregalarty alternat-

Lag lighter and darker bande,,,------d------888 Ckrm gray maatone--,,--,,---, ---,,,-, -,,---,---- 80 Bmded asglLEaceous amdstone Mtb Belmdien-,,,,,,,, $00 Coam may sandstone with Bahndteu,,,,,,,,------40 Banded arghmns ~and~twe,------,,,,,,,-,,,,,,,--,,,, RB Coarse gmy ~~ndstorieand Ane conglomerate,,,,,,,-,,,,,, 36 BanM argllIaceoa6 mndrrtone with wved iaaulllfanrtlil Ma, and a few thh bands of Rne con~lomerate--,,,,- 158 @ornewbatmaeelve dark-gray arglllaceoap Randatone Hth a few thin yellawlsh bands,-,,,-,------,-,,------1M

Conw&g this &ion Martin ssp that the gmat thickness may pomib2y be due to repetition of beds by f adting but th~tno mpeti- tiona were dektsd. 'She exposures of the Nhek formation between Chinitns and Dry Bays confirm the measurement on the north &ore of Chinitna Bay and indicate that it is not nwdytoo

RIa hk- and&& &atone, conglomerate, and Wr, 2,000" Z Handy uhnle wltb dwdb nmr base-,, Wl & Elhale with fwdla ,,,,,,,,,,,,,--,--,- a&0 6. Coam nambtone 3 tirnBhaIe with Car&-, $st&, and omfmdle,,, It35 0, ConceaIed 40 7. Randntone and sandy sbale with Lytmwaa, mZbmas, and plant imprewiom-,,,,,,,-,,-- 310 k Uonglomerate with an abm8anee of mall peb- me twelfth to omtwenty-fifth inch in length, and wItll numerow poorly prmmred fmpmslons of plants,, 7 9. Sandy shale and sandatone-,-,,-,,-- &LI

D. Fine conglomerate of trame pebblwi srrr above-,,---,-- 5 13. Flne conglomerate of mme pebbles IW above, but Inbr- bedded with We--,--,--,,,,,,-----=------14 14. Olive ahah with an abundance of &I p?bble& and wlth indeterminate fragments of a att&acenn 6 feet above the barn---,-,--,-,-,-,,,,------80 The beds nnmhred 8 to 14 ara probably the Idrepresentrttivea of the Chisik conglomerah member. This part of the mtion in- dndm the beds that Martin considered to be the local representative of the Chisik conglomerate. Beds of this kind are pmnt on the mthshow of Ghinitna Bay end e1sewb.e~on the peninsuIa and are regarded as merging the base of the Naknek formation. ABalready pointed out (p. 881, beatme of their lithologic &flew= they were not deaigneted on the plogic map (pL 2) as Wikconglomerats, although they are considered to be the time equivalent of it.

&w&n of tounw pwt of Rabnek fwrtlatkm on emt 8hore of I&Ms BoV* dbnb A$et $andstwe, arbable, andmite flows, and cwglomerate-- W0-k Dark -Q &aIe with kucelb in upper pad ,,,,,,,,,, , Martin m&ea the following statemsnt concerning the beds of volcmic material associated with the other be& of the Nhek formation : The betin described as andeslte or a# andealtic tnU In the above Woware ctmm of fragmental material. The microscope reveala fragmente &d -tala oil plagloclase (aome of which were determined to be baElic). hornblende, blotkte, an8 Quartz and also Borne blts of flnegmind Igneous mkSL &lof thmw are predominantly mgular In ontline, but a few are rounded. The matrix In 8ome ~pecirnen~Is dlatlnctly fragmental; in othera it ia so fhe md Iron medas to be obacnre bnt la probnbly aleo fmgmentnI and corn- of the same materials aa the other SmImena. In one apecimea slightly c-r than the rest, the larger gmlns are well round&. The claklc, angnlar, character of the grdm of the roch and their MrnpoaitIon leavea no dmbt that they ere t&a derlv& from mdesitlc lavae. The fragments- of rmk Ere tcw ilne gr&Llled and too much mthend to be determined but seem to be basic. IntMigwow mh.-Ln addition ta the bedded rock, made up in part st least of the frsgmenbl volcmic material just mentioned, & Nab& formation is intruded by light-colored granita gills and badtic dilres. hkof time prevented a thorough examhiation of the upper part of the formation, m that other igneous rocks than tbrnre menti.oned may be present without having ;been noM. Several sills were seen near the base of the upper part of the Raknak formation on the east side of Oil Bay. Two dls of qua* diorih, one 10 inches thick end the other 2 feet thick, are intruded batween beda of sandstone just below the base of the white beda The mck ia light gray and fine grained but still suflicientIy mares for biotite, hornblende, quartz, and feldspar Ito be distinguishable with She unaided eye. So far aa okedthe silts ere dmctuFally Mrnfmable with the sandstone beds and resemble the ~rkp9icsand- gtonea that m misted with them md that occur aIm in the lower part of the Nahek, mi that only by close examination is- their pree- ence de-d. Thin sections under the microncope show labradorite feldepsr, biotite, hornblende, quartz, apetitg magnetite, and chlorite. The groundmass consist8 essentially of feldspar and hornblads. A second sill is pment a short distance stratigraphidy Mow the pill just described. It abo ia composed of light-gay quartz diorib which is rather #am grained and shows feldspar, quartz, and 1-n4 PgrOmB, The gill is intruded sa a thin shwt into bectg of srsnd- heand mndy dude and in structurally conformable with them Thin &ions under the microscope show make, augib, hornblende, quartz, sbundant mtqnetite, a small quantity of apatite, =- ondarg chlori* and iron shins. Phen- of feldspar (andesine), sngite, hornblende, and quartz appear in a granular gronndrnm Tha rock shows, little alteration, although mechlorite has developed from the hornblende and aygite, and iron stains are present. t Martin reports that two basaltic dikes cut the Hahek hmlstticm on the shore of Gook Inlet between Dq and Oii Bays. NO other dike, of this kind were noted in the Nab& formation. I Ags aderne*-Fossils are less nvmemns in the sedimentary beds of the Ndmek formation than in the underlying Chinitna shds and the Tnxedni sandstone. The basaI Chisik conglomerate member has furnished no fossils, but fossils are abundant at txrt~in horizons in the Naknek and yielcl conclusive evidence that the form5 tion is of Upper Jur~lpsicage. More than 20 sp~iesas identified by T. W. Stanton are contained in the fuIlowing list : IOgaS. F 20. Wed aide of Oil Bay, aboat belt a mLle from head: Amticas 5p. Cardioceras martini ILeeslde. Mwer part of Nlrlrnek formatlm 2MM8. AB F 2. Bmth shore of ChhEBm Bay in the lower part of the Waknek formatkon abont 200 feet above aswmed kw: ThraciaS ep. Revernl mall undetem5ned pelecypotlr~and PhyUaceraa up. Preeamablg Nah€& but foatdla not dbtfndm. 11M)la. AB F 9. Sonth more of Wtna my, lo Wun, probably from lower part of Nahek formatian: GoIlfomya sp. PbylIoceraa ? sp. Young shell. Fmdls not diatinctlw. 5 n002. A13 F 11. douth nhwe Q? Chinitan Bay, fn tsltta, pmb4 frtm Tower plrt or N~Wiormauon : Oardim marM Re&&. CardlmIUIooetenie Redde. C Lower part of Xaknek formation. UOOBk AB F Ik Sonth shore of Chbttna BaJ, In taItra, p~bablg 1- 1- plrk of NaLwg fOrmat1m : Amtica? sp. Plenrawn np. Gonfomya osp. Fossli~not di&JncUpe. 11013. AB F P1. Booth ahom of Wltna Bay: Fragmentary plants. CardimwrM &tans (Whlteald). Lamer part of Nhek formiltlon, Aetarte rrpc Plenromya rrp Corbnla? irp. Phyllaceras, sped- Cndacerm mmttLni Reed& Cardwas atf. C. &tam [Whield). Cardioceraa mmetezle -da Uwer part of Nabk formation. 11MS. bB F 25. Sonth ahore of Chfnftoa m: mfla BP pnSlloee?adl pp. Larm dl&. Icower part af Naknek fomnah. 11- dS F 61. From taEm below contact d Witna and N&ek f- W; 8,400 feet npcreekleamg to peakeast of CY peok: Cardioceras n. ~p. Lower part of Nabek formaIon. fim AB F Bg and 67. Near contact of mtna &ale 8nd OhMk congl~mm nbe member at smdgoht dawn 011 Bay from gava pit nem Bomr M: Plant fragmmta mam. Arctica? ap= PleuromgtL ep. Thrncle spc PhytlWflB sp. Cardlweraa martlni Rewide, Lower part of N-ek formation. Al3 Ir 69. Nalmek formation. Ead coast of 011 Bag N. 81' a. of Mount Pomeroy : Pbyllocemr m. CarRiocernn atr. C. dim tan^ (Whitfield). Lower part of Naknek formution. Them collectione, as well as those of Stanton and Martin from the vicinity of Chinitna and 3nisk-i Bays given below, were made from beds in the lower part of the Nah& formation below the mas sim diR-farming beds. No fossils were collected from the upper member of the formation on this peninsula. M1 the forms of dimtmu~in the list are themfore from the lower part of the Nnknsk, where, although not abundant, they are common enough ta ba of great ammin drawing the fomtion boundary. Two other species, AdbpaUas%' and AwUu bmn+ or forma cIose1y dated to them, are ~hcharacte~c06 the Nhek formation but do not appear in the list just given, porwibly busre less the warr given to collecting from the upper-bedsof the Nahelr formation than from the formations below the Nakneki * One cofldon of fossiI plants, made from beds on hiskin Bay, kgnd to the Nhek formation in the'field, was debrmined by Knowlton as follows: 7 7525. Nakuek rlormation. About 8,080 feet aouth along east &ore of Id&h Bny from end of trail at lower cabin: A mall hgment of NBlmda me N. orhddb Heer, but too mnll to be cerltah. The collectiom of invertebrate foaslils from the Naltnelt formstion, made by Stanton and Martin during their investigetiom, contain meadditional forms and am therefore given : 8022, North shore of Chhitna Bag, onefourth mfle mst d mouth d W Qlacler Clreek : Belemnites. Aucelka et k errin%& Avlcula -ten tmd other fCmm 8028. Chinitna Bay. 2B feet aMve baae of KO.84 of &on : Ph~Ua!eTam. Belemnltsi. Plenrompa CyprSnaP agtarte. Pecten. PInna. Enmlcrotm? .MM. Chidtna BaF, 30 feet ahve hbase of No. 54 of Wn: Pbyllocerta Plenromga Corbula 7 Avi~dk ' Und~termhedgnat-& ~er'ysmaU BIB. Chinltna Bag, No. 28 of Won: Pecten. Avlcula. hca and other form& 802& ChiniOm Bay, No. 26 ot Won: Phyll~cerm ' mlemnitw. Andla. 804% Chiultna Bay beed (~i&1 ~~ekaba*e gadmuma none: hrrtarte, large sp. mLmwbkin Bag, on dore of Idakin Bny; &st cope on erUrt Bhore near eutranw to bay: Ancella d A errlngbnl. Belernnlh. EaatdmmOt WBay: 16feetabwebaeednio.UM&n: - Lytooer8& fmmnmts of large sgecles. Belemnitee. Pleuroa Wniomya. $oar, Oil Bay, 270 feet &mebPlse of No, 11 ;not in place : Cardiowaa 8p.; hedptnre, tf. i.. altemus, C. erne,d &Mum Hyatt, and 0. whiheyl Smith. Tbracla BS; short form. W)aS. Oil Rag, 80 fmt above base of No. 18 of se&Iom : Wrdloceras ~p.; mare sealptrtm Pbyllmrae. Avicnla. Astarta Oit~,~f&abm~dNo.18ddm: hrdimra~; mame mlptnre : snme m 9942. Plenromya. 8047. 011 Bay, 700 feet above We of No. 13 of don: Irptooeras : not collected.. Pleuromya. Ancell a. The type locality of the Naknek formation is the ~chityof NalBnelr Lake on the Alaska Peninsula. The bsds were first dmribd by Spurr,iBwho says of them : The N-ek eeriea eollgLLlts of a gmat &lchaeas of grdh arkasen and ccm- glomemW, which generally concala pebbl~of panib. AU thew Mhentary mka are evidently derived from the deatruction at a land msm which eon- uMed largely of hornblende-bfotita granlte. There = probably some volcanIe intemtmtLUed wlth the arkaee and eonglomerab, although It b not abeo1utelg proved that those examinerl may not be intmsln 1 These rocks- throughout the mrim contdn abundant f& and in aZ? but one of Spurn's localities yielded a qmim of A4 Beds belonging to the N~hekformation extend north- of Y Nsknek hake md are widely distribntd in the vdegs of Sad and Kaarnishak Ripe- where they were stndied by In the Cold Bay district the Nhek formation consists of conglomerate, arksic sandstone, and sandy shda ne described by Capp~.*~!f'his &ion includes rt badconglomemtamhich mgea in thiches from 70 to 1,000 feet and which is Wieved to ba the equivalent of the Chi& conglomerate member. The whole mom- sion of Nbek be& is more than 5j000 feet thick.

*am, J. n,d mm3mme In wntb-m klaaha in 1898: U. I.Oeob. Twentleta Ann. Be&, pt. 7, p. 170, 1800. -Mather, K F., Ytnetml mourms of tha ndmb*L Mm:U. 8, W. my M.773, pp. 189-111, 1926. * Cappa. 8, R., The Cold Bay dlsMft. AI-kl : f7. B. OmL Bmty Ban. 7Sd. I. *a.1W2. Dppw Jnkcm?m that carry the fama of tha N&mk h- tiun rnxar in Matanuska and MelhVdleys, in Chitina Valley, between Nabme and mi&Rivers on the east side of the WrangeU Mountains, on the Arctic coast, end in southeastern Ma&. The Cardbcera fa- in the lower pert of khe Nahek formation of the Iniskin-Chinib PeninsuZg, however, is known from only two of the &strich wham Upper Jurassic faunaa have bean mUe(:td-that is, from &a Cold Bay district and the Upper MstmaSg, and Nelchim Vdeys, Tbe Iudities and lithologic charm of the Upper Jurassio formations are given in tho mhtion table opposite page 22. QUAWART The unm1idaM depitrc of tba ~~-C~Peminsula include &-plain deposits, Btream and bench deposits, md glacial depita. Among these, wastal-plain and stream deposits much more extmsivaly developed than depasits msulting from glaciatioa Coestslr gram1 md sand form a narrow band, limited by high tide, along the ouhr shorn of the psninsula but are mmewbat be* 'developed within the hap, where they are petedfrom the ertrong cnrrsnts of the inlet. The marahy flata on the mutb aide and around the head of WtnaBay (pl. 10, B) are in parf built np of marine shore gravel intermingIeCE with gravel and sand contributed directJy by &reams md with accmulations of vegetable mstter. The flats amend Camp Point are of this mime, as am probably aZgo the lowlands at the heads of Oil and Dry Bays, Without doubt the ses at no didant geologic time axtemded much hrthe~into deyalike that of Bowaer Creek, Wblycutting off the mounhbetween Oil md hiskin Rays from the mt of the penimls, and leaving marine deposits on the valley doors an its =treat. De@ts of this End, however, would be subjact to more or less ~ributicrnby dmanu md Mbly by glaciers and anmy no longer remain. No gsvd of marine origin wrrs recognized except dong the shore link The deposits of stream and bench gravel are bere mnaidened together because the only bench gravel man ia but a few feet above the level of the mar-by stre&ms and wlus quite evidemtly laid down by the dream. Deposits of pveland mnd are less omonin this area than in mnch af inhrior Alaska and are &&d to the flood plains 02 the strenms and to the adjacent dley floors. The deposits are mostly of local origin but contain erratic bodders, which were doubtless brought lm their pmtresting gl- by ice moping from the high mountains west of this nma. Owing to the rapid waather- ing of the shde that ompies a large part of the peninsula within the bounding zone of the mdstone at the top of the Nahek formation, the st- and beneh gravel contains much srgillaceous materid and pa& down so rn to mahe mep& deposits that fnrniah fwting for howexcept where they are poorly drain4 &I the grass-covered Bats at the head of Chinjtns Bay. Qnicbmds were not found in my of the streams traverd during the summer. So far as known, the dream gravel nowhem contains goId or other valuabEe minerah The readiness with which the shale and sandstone ~~teand tse ME with which the resulting 1- material ia w amid away by the stpeams am probably the principal mamm for tbe lack of mspicbons gravel deposits in the district. In spite of the fact that ice must have once covered m& of tha mnsula, glacial dewsib are notably mwrmnon and were recog- nbdonly where foreign mbid was swn in the loceZ stman gravels. The mmmon topogrsphic expressions of glacial deposits were not obsarped, although they are evident in neighboring areas and may once have been present here.

The structure of the wdimentary beds of the peninsula has twen indicated in the descriptions of the different formationel, but a sum- mary of the features will be given in order ta present this part of tbe geo10gg in a more convenient form. host 14,000 feet, of Middle and Upper Jurassic sedimente were deposited to form the total thickness of beds represented in the stratigraphic section. Presumably dl these beds were leid down in s practicdly horizontal position, but their original attitude waa altered by forces that prduced in them a m&on of folds which am more closely mmpdon the landward side, of the peninsula than on the detoward hkInlet. Two principal anticlid folds dEed fmthe deformation and trend about N. 30" E., parallel to of 2. L tha trend Cook Met. These folds are shown on Plate The axis of the gmaller fold Iies along the east side of the Portage Creek Vdley but is cut off midway between Right Arm tsnd Chinitnil Bay by a great fanlt, which extends far many mila dong the west coast 4 of the inlet and mpsrates the Tux& sandstone of this district from the Lower Jurrtasic ( 2) voI&c rocks north of Jhiskia Bay and wed of Portage Cmk The axis of the main antidine of the peninmila atads from a point between Oil and Iniskin Bays dong the west ide of the Bowrser Creek Valley and through the Fitz Creek Vdley, but before reaching Chiaitna Bay, it divides into two minor anticlinal folds, as shown on the geologic map. Chiaitna Bay intempts the dhentary beds north of the penbda md concesls their struc- Itnre, but the beds appear wain on the north shorn of the bay near its mouth in mch m way as to suggest that within the amof the bay the folds pitch gently northeastw~rd. Between Oil md Iniskin Beya the main 'antiche ia camp-d than in the Fitz Crwtk Vdey and flattans out into a broad, fltst arch. Thk flattening of .the ~~B is well ahawn along the east shore of ~~ Bay northward from the wagon road, for although &a expusures are continuous for severd miles only a slight thickness of the Turr~dnisand- stone is exposed. The structure in this vicinity, however, is cmpli- cated by an eagtward-trending fault, transverw to the wig of the mticlin~,whose exact location is known only where it appears on t the shore of Ininkin Bay and whose displamment is of such mi@- tude that beds believed to belong below the middle of the Tuxedni mndebne, aa shown by their lithology md the stmtigraphic &ion a few mila l;o the north, brought into contact with the Wnitna * sMe, thus mtting out possibly 3,000 feet or more of upper Tuxe sandaone beds. The synclinal axis between the two principal anticlines is remarkably straight ~ndin the vicinity of Right Arm is less thsn half a mile from the Portage Creek anticline. Ea& of Bomr and Fitz Creeks the Tuxmini sandstone and the overlying Chipiha shale and Nakneg formation, including the Chkik conglomerate member, dip away from the paninsuls toward Cook Inlet. The atrjke of the be& changes from &-northeast at the mouth of Chinitxla Bay to nearly east & Tniskifl by, md the dip dimjnid~eafrom a maximum of 45O north of Mount Chinitna to about 15" at the entrants to Iniskin Bay. Minor .folds are probably pmsent on the east limb of the main anticline in tha area between Bowser and Park Chek~.This area was not exmined wefuUy, for thewm lacking, but one mall fold waa mnin the lower park of the Wtna shale on the larger headwater branch of Bowmr Creek, and the presence of oth~rminor folds is suspected. The fold mentioned is a mall anticline crossed by the cr~kand exposed along the west bank to its full extent within a dishme of not over 800 feet. The folding was ruxompanid by faulting, which caused w much disturbance in the shale and concretionary sandy shale of the locality. No evidence of the fold was recognized on the adjmt streams in the direction of the strike. * Rafemce has been made to the fault between the Tuxedni sandstone and the volcanic rocks west of Portage Creek and to the east- wad-trending fault between Oil and Iniskin Bays. The fadt between the Tuxedni sandstone and the Lower Jurdc (8) volcanic rocks extends through the vdey of Portage Creek and throughout most of its lmgth is ooncertled by vegetation and unmmoLidatd material on the valley floor, so that direct obeervstion is rarely possible. In some places it is evidently formed by a sumemion of parallel, vertical fnults. Locally it hm produced patdisturbance of the beds, as is particularly well shown in the small biU projecting into Iniskin Bay wuth of the entrance ta Right Arm, where the sandstone b& are broken into blocks and &&en up so as to d&oy a11 evidmce of the original stmctnm The exact trend of the fault between OiE and hiskin Bap b not known. Possibly it awings to the nortW and connects with the hdt indicated on the nap as mtendmg parallel to Bowser Cmk on theeast side of the valley. This fault wasnot obrved in tha field, but its presence is infer& from evidence furnished by the stratigraphic sectiow, for there appears to Im too little mrn below the Chinitns shah in this vicinity to provide space for all the upper beds of the Tuxedni sendstone. This fault may be of much greater extent than is indicated on the map. Many srnlall faults were observed during the field work. Some of them suggest considerable disturbance of the adjacent rocks end are shown on the map where the data are available, but undoubtedIy many othexs mxe not detected. The bds traverwd by some of the faults are conspicuously jointed. Two prominent vertical faults that gtrike N. 90" W. on the west shore of Oil Bay are accompanied by dody spaced parallel joints. Simi- lar jointing is sem on the east shore also, and in exposures of Tuxedni sandstone along Bawmr Creek 1% miles north of Oil Bay it is con- apicuous because of the unusual regularity of the spacing and the pmnca of horizontsl joints, which hogether with the vertical jointa3 give the outcrop the appearance of masonry, The position and form of Oil &y are doubtless direetIy due to this combin~tionof fdts and joint planes, for the clam fracturing of the rocks would make them pdicuIarly susceptible to attack by the sea and to the ~ction of streams and the weather. A similar cause is suggested for the formation of Dry Bay and lower Brown Creek Valby,

The amliest events in the geologic hidory of the area between kiskk and Chinitna Brrps that may be learned from €he racb expsed there go back nd further thk Middle or Lower Jur-c time and are revealed by the volcanic rocks that mpom the mcnui- him west of Po* creek Thew mountains fo& the aastern front of the Chigmit Range and lie in a belt of vole~cbeds, including. both tuffs and flows, which extends for many miles along the west eide of Cook Inlet. Amygdaloidal basalt and-vol&c agglomerate am among the more characteristic rocks of this serieszs On the we& and north shores of Inisin Bay basalt, gabbro, and tuff are pmenk, and at the head of Chinitna Bsy olivine basdt snd tuff %re indudd among the volcanic roch According to Martin

'MnrtIn, a. C, and FWa, F. I.,A gaologlc reconnalsemcm of the nlrmnr redon, kh : U. I. Q~OI. EUW~YMI. 485, p. al, 1012. and Katz the ~olcanic& overlie the Kmbhak chert (Upper Triassic) of Kmnkhak Bay and in the abmnm of positive evidence for their age were assigned to the berJurakc. The volcanic mcks of K&sh& Bay overlie conformably the thh-bedded chert, black calc~uashale, and impure limestone which compose the Eamish& chert adindicate that the period of marine dimsntation represented by tbt formation was m(x8eded by a period of great volcanic activity, which is represented by a wide distribution of vol- F canic rocks in muthem and southwestern Alaska, but which was no* hown beyond the Alaska Rmga. In Middle Jurwic time the dhneatary be& of the Tuxedni ~dstonewem laid down; The cmgfamerates and arkof the lower part of the Tuxes sandstone indicate that they were derived from a near-by Ian. rnw toward the we& This land mass was probably s region of high relief, where the streams vigoroudy at- tacked the pnitic rocks of which it must hrrve been in considerable part oompod, for the coamgrained material of the arkosezandthe pebbles and boulders of the mnglommte in the Tux6sandstone consist largely of cloarse-grained granitic rocks, although they in- , dude also volcani~rocks. The coarse-grained sediments of the lower 'Snxedni beds are sne ceeded by shale and andm sandstone and a few d limestone be&, which were laid down in quieter waters, probably with la*roue action of the irrtPeams on hdor else at greater dihw from the &ore. De@tion memiqlp continned witbout intemption from Middle Juraasic time into Upper Jurassic time, when the Chinitm shales were famed. The more homogeneous character of thw shdw mg@s quiet waters in which the fine mud ac3rmmuIatad with only subordinate admixtures of sand but with more calcareous material than is found in the Middle Jurassic be& f The Chi& conglomerate member of the Nh& appears te have been laid upon the Chinitm shah without a atfuctural break in the wntinuity of beds, but in i-lf it ts8prems a variety of conditim of mdimmtation that dX& widely within short distsncea The b co- gravel md boulders of the Chi& oong1omerata on. his& Bay tlnd at the type locality on ChiGk bland indicate deposition near &ore. On the shorn of Oil Bay Bna thence northeashad to Ghhitnrt Bay no such conglomer~teis p-t, but in itEl plw that is, between the Chinitna shale and the shde and mdstone beds at the barn of the Nhek formation-there am be& of grit and ark- which seemingly are con~pormmuswith the conglomerate. These beds grade into the overlying finer-grained ssndatone and shale beds of the Naknek fomitior~ A change in the End of material brought b the Upper Jurassic spa was marked by the beginning of the depwiti0.11of the &ve iigh~Io~sandstone beds that make up the higheat part of the Nh& formstion in this district. These b& are composed of a considarable amount of tuffmeom material, which indicates that volcanic activity waa again resumed after an apparent lapse that cantinned from the herJarassic well into Upper Jurassic time. The formation of the light-colored sandstone in the upper part of the Nth& fornation completed the Jurassic sdiment~tionin this rl. paninda. No evidence- of younger consolidated sediments was found, although Tertiary bedg are ex-d on the north shore of =tna Bay at the mouth of East Glacier Creelr. * The next great event in tha geologic history of tbe amwss the eftand fol- of the Jurassic sedimentmy bds, which were rubd abow the sea and hams subject to the prommw of weather- @. Evidence collected in other parts of Alaska indicates that thin apWt began mme timg after the end of the Jurassic perid and mntiaued well into the Cretaceous. The folding and uplift wem not necessarily continuous pmcmses and may not haye prdedsimultan~ousIy, but together they mark the begking of the development of the present topographic form of the area. Erosion of the rising Imd began the formation of vslley% and uplands as they are at present distributed, but was not &a mle agent in their formation, for the normal promses of &ream emmion and weathering were modified by the advence of glmial ice from the mdand. This ice was of sufficient depth to spill aver the ridge between Portage and Fitz Creeks, as b shown by emtic: boulders, and probably flowed fiam Bight hto Oil Bay, for the highest pint of the depdon between these bdies of water is only 100 feet above present sea level. PmibIJ the ice mcupied the Brown Cmk Vday also, although the form of that valley does not sug- gst exbsive glwiation. The soft, rapidly weathering shg]~ t thrmgh which Brown Creek flows am, however, not well adapted for p-ving the topographic forms cramed by the ice. In its major features the area probably does nut now present an 4 appesrance greatly different from its appearance when the ica re- ded, although the evidence of many locslities on the coast of Alhindicates that changes of sea level may bve odsince that time md that them chaap were of dcient ammt to have brought the sea well inta the lower valleys of the &reams at Oil ' . Bay, Dry Bay, and simiIar plawrs. Glacial streams have contributed and are now contributing great quantities of silt and gravel to the heads of Xniskin and Chinitna Bays, where the material is exposed in wide gram-covered lowlands above high tide or in mud flats at low tida So far rn ie now hown, petroleum is the only mined mnm . of the peninsula between Iniskin and Wtna Bays that o8es a pibility of profitable commercial development. In earlier years a few pmspchtors panned the stream gravel in the search for plmr gold, and examined the hiIls in the hope.of hdhg gold lodes or R deposits of copper or other metals, but without suocess. Petroleum seepages, however, were hown in the vicinity of Oil Bay mang gears before the great rush of gold seekem to Alaaka after the dh- coveries in the mandike, and attempts hve been made to prove or f disprove the presence of an oil pol. The work met with .incon- elusive rermlts, although a number of wells were drilled, and was finally abandoned, probably from lack of gems for continuing itc

The indications of peh1enm that ht dirwtd attention to the possibility of obtaining oil in this part of the Cook Met region amspringg or seepages of oil and gasgaefMmy such springs have been reported and have led to the staking of numerous claims in the earlier days before the oil lmds were withdrawn from entry &id winin recent years after the leasing law of 1920'wns pd. The writer made an &tempt examine the geepages that have bean reported, but in the absence of anyone familiar with their exact location, he did not fully accomplish the work Martin reports a strong ~psgebetween high and low tidm on the east shorn of bigkin Bay, &bout 1,000 feat below the lowar cabm, which produced an intermittent flow of oil, at one pram corning from s crevica in the shsle of the upper part of the Tnxedni sandstone. 9 No sign of this seepage was seen by the writer, and possibly it haa been diverted or is exhausted. One is of the oil seepages at Oil Bay st the foot of the hill, about * 100 feet east of the place where the OM mad from the mbin i?tarh up the hill to the fourth well. The oil Fim in s spring of water and collects on the surface of the water in a amall pl. At the time the . place was visited in 1921 not mom than an ounce or two of oil mu18 be taken from this pool in a day. A strong flow of gas, bubbling up through water, about 2 miles north of Dry Bay led to drilling at that locality. Oil claims have 'been ataked recently on the ehm of Ckinitns Bay, where oil seepages am also reportad. Although the south shore of Chinitna Bay wsa examined Tather carefully, no seepass . were fmnd there by the surveying parties in 1921. Oil springs might w9y k miseed, however, unless their lomthn was fairly well known, fox &be vegetation by midmmmer is rim rank 98 tO hide 8h.enrr. The hwn-pagas;, with the exception of the gas spring st Dry Bay, am within tbe amrr of the Tuxedni saxldstons, and their presence probably depends on the fect that the rocks where they ~wurare fauIted or conspicuously jointed, thus giving m oppor- dxnity for oil and $as to escape to the surface. *I EXFWRATIOW AND D-0 Oil Bay and its viciniQ was viaikd by Martinz0 in 1903 and * .again in 1904, during the tima when drilling operatioas were in progress. Matin's reports on his investigations msde at that time are the best available source of information on the devebpment of the Mckend the character of the ail seepage and am ud freelg in lhia xprt. Martin states that indications of petroleum were discovered in -the MhBay region in 1853 and that the htsamples of petroleum were taken by a Russian named Paveloff in 1882. A mttn named Bdelman &ked claims near the heads of Bowser and Brawn C& 'in 1892, but these claims were not drilled and apparently no work af any kind was done on them. Pomeroy & Griffen staked claims mew th head of Oil Bay in 1896, organized the Alaska Petroleum 4%. in 1897, and began pieIiminary work on the ground in 1898. Ddhg is reported to have bean in progress in 1900, although OLiphmtm says that the well at 03 Bay was started ia 1902, after mmgsful attempts had been made in 1899 t~ land machinery arid in lsO1 to begin drdling. Work on the &st well, half a mile from the by,near Bowmr Creek (pl. 2) was ended in 1903. Martin was unable to get authentic information about this well s but states that it was said to be more than 1,000 feet dq,that gwi ww mmunhred dl the way below 180 feet, and that eonsiderabb oil WM found at a depth of €ither 500 or 700 f~t.It improbable

.r that the reported flow of 50 barrels a day was actually obtained, although oil was andoubtedly present. men the well was &drilled deeper ta strong flow of salt water shut off the flow of oil, Efforts b recover the 02 or to drill deeper were not mcdl. At pr-nt w8tex flows from the pipe and through it pabubbles continually, but practicdy no oil accompanies it. A mond hale was drilled in 1904. near the bttse of a ?dlthree- bths of a mile northwest of the khwell. and nearly-400 fwt -- - rMadn, 0. C., Ttre pekolwm fields of the Pacific coast of Ala&a: U. 8. W1. Sam Bafl. 260, pp. 87-48, 19W: Prelfminary report on p&oleum in AIaskn: U. El. Qeol. Sarpeq Bufl. 110, pp. 61-65, 1921. Marttn, O. C., itnd Kn& F. J., A recrmaal@eancaof the ZHarnna reglow Alaeka: U. 8. Qeol, Bmw Bull. 48h, pp. 128--180,1012. m-Qllphant, Xr. R., Petroleom: U. 8. GmI. Snmy Mineral Resourcm, 1903, p. BB1, 19W. north of the mad to Inialrin Bay. When this well bad reacbed a depth of 450 feet it wag abandoned becam of sM8. The lag of the well, ~rafurnished by Mr. A* Bowser, who had charge of the drilling is as follows:

Rccota of WEZF NO. 2 at Oiz ~ay Fet Sandatone,,-,,--,--~~~------H@

ahale-,,--- -,,,,------m-m------120 Oil and Borne gaa -,,,,,,,,,,----,-,------,---,---1

shale (caving) --,,-,,--,,_-, l2W

A third well was started in the same pratmost directly 4 of the second well and about 150 feet from the road. It was sunk to a depth of 900 feet but was cased for only 630 feet Caving ground waa encountered at 880 fwt. At 7'10 feet three oil mnds 6 to 8 inches thick and 4 or 5 feet apart were pdthrough. Ac- cording to Mr. Rowser the well produd about 10 barrels of oil a day and had a gas prmmre wfiicient b blow water into the derrick to a height of 20 feet.

Water now flows from the pipe in this well ht in 1- amonnt thm from the first well. A little gas md oil ahcame up the #ipe + wit6 the waDer, but the qmtity is less than that in the naturat sepage at the foot of the hill a Bhort distance to thn &- A fourth hole was started on the low hill half a mile ndof the cabin st the fir& hole The derrick is hill &amding. No information concerning this bole is at hmd, The pipe m plug& and no evidence of 02, gas, or water was seen when the place was ~isibdin 1926. No drilling was done at Oil Bay after 1906, and in 1909 the chwere abandoned. - Drilling operations at Dry Bay were undertakan by the Alab Oii Co. st about the same time as at Oil Bay. This company was organized in 1901 arid began drilling in 1902, The; fimt well was put down that year, but the tools were lost at a depth of 820 feat + without obtaining oil, and the hole was abkndaned. The well had a diameter of 8 inch- to a depth of 812 feet and of 6 inches below thet depth. A second well was started in 1903 near the first but wag soon abandoned bemum of an accident to the rmdimq. No other drilling was undeden at Dry Bay after lsQ3.

GHAFumER OF TBX OIL The character of the oil from the principal --'at Oil Bay is described by Martinpl und as the opportunities for mlWiam-

albartln, 0. C., Prslfminnrg report on petroleum in Aha-: D. 8. W. $017- BdL 718, pp, 6W1, 1821. plss wmldm at the heof his Gt than they wem in fml, no athnpt was made to duplicltta his worb The following datematt is quoted from biQt dearription : A~ampladgetr~lemnfKlmtheseepageat Oil Baywtmmlectedbgthewrlt~r bg tWmmhg the oil from tbe dace of the water, where it was continnaW ddng from the bottom of ithe POOL An effort was made to obtain as mncb of the iresher oil as pr#rhiible. V-Cable and earthp fmptwftiea we= removed by G 6htning thrmgh coarse cloth. Water could not kw entirely remod on for ~obrlcattmat the neighboring welh has been obtained from the gooh h thJB mamler. ~e~heroUL~k~TbatwhZchhaaremaIaedonthemmfaceof * tba pool for mme time fa aark brown. The oil bas donbtW lost a large part of Its vo- dtnente, pa that the aW~ie%do not represeat the compofdtion of tha Uve ofl from wells in thia regla Bnch Uve wonId have a lower specItlc grad*, a higher mtage 3 the more volatile Nw%tlhent%and a lower mrce~tmof tb8 1,8cis volatile dhents, ddne, and 8alphm. It woald oa~titlnlybe better than thean -flea in a re~wcb~an& would wblethem in bavhg a pa& base aod would danbtlw be a mfhIng oil. Tl& sample wa@wbmitted Do Peuairmtll% Bme,of Baltimore, who retaFn the foUowhg report on ZheIr testhl:

mb~Egm'omethod: Bnmiw oll ( blUstim a ta 3000 0 mQer nhmma ~aLamcaMnsom ,,baa ohwo miiumbr np to m kj:~::::: Labrfmtj oila $W~nill!meter tm, ..-..--,-...... --.,. 17.0 Pnmtb G% ((bydadtrmctivs &%%on Undsr WWom) -.....-- 22.4 BRI Gahand la.,..,,-...-....+--.-.------.------v-+*-----.---*.------. 1m.O ...... am

w~dtyotmwkd1abW F., kW7, ,wlMeBnu&. Mtfalbfbgpoint,W C.

& The bbrlcating oils were dlWed under diminishing pramme, ~~g to pmdce, untn &nri of decompohntion 8et in, The &due obtained wm rtnwitable for making cylinder &mk Imd waa therefore dktllled for 4 pmafb om. Thew param oils contain a conalderable quantity of golid pr-n-how much it was not practicable to determine with the mall qnantlty of! oil M. The iodine ab@on d the o& and dlstlllatm waa determined by Hanus'a method ~mIutlwsWdIng 4 horn 1 and ie here tabulated :

Per ceat of iodiae Burning &-,--,,---,,,,,,,,-,------,,-,,,, 17.8 Lnbrlmtlng oil - -,,,----,--,,---,,---,,,,,,,--,,,-,--,2& 2 Heavy lnhrlmtlng 0% ---,,----,,,---,------86.8 Iadia a1nomtbm oJ aommerald oCk Pbr mat of lodhm Light Maddubrlathg oil (spindle dl)------m.0 Dark lnbrfcating oil (engine 011) ----,--,------45.4

The burning oils were tested in a mall lamp and found to give a W C flame. d11 the oil wm corn& wlthout ZncrnBthg tbe wfek OF cormdhg the burner. The oil has a para5n barn, and the prodnCts & dietllhttmi are. We are informed that thia mmple h a seepam dl." It a wiBefent field can " t be obtdned by drflll~g,an oil anibble for reflning may be erpected, mntahlng d very much larger quantity of the more deslrnble If~bterprorlucts.

The oil -pages and drill holes showing oil are within the area of the Tudni sandstone. 80 far as is known none of the seepagw,' except the gas spring at Dry Bay, are within nreaa of the Chinitna shale or the Naknelr formation. It is therefom believed that the source of the oil is within the Tuxedni sandatone or Wbly elt Borne lower horizon. Two of the drill holes at Oil Bey are reported te have penetrated oil-bearing sands at depths of 600 and 770 feet and to have shown a considerable quantity of oil. Thw fipres indicate tba minimum depth below the top of the Tuedni mndshne at which the ail-bearing bds can lie, but the evidenca from this source is made highly inconclusive by the probable existentla of an eastward-trending fault of considerable vertical displacement between the drill holes and tha mountains on the south. This fault is expsd on the shore of Iniskin Bay, and if it exfended eastward ta Bomr Cmk it would incream rather than decrease the estimate just given. It appears probable, although it ia not dehitaly proved, that many hmddfwt of the sandy ahale that forms the upper partof the Tux- edni esndstone is missing between Oil md Iniskin Bays md that the oil =pages and the oil from the drill holes may well come from a C horizon as low as the middle of ths Tux& if not lower. The oil mpqpin the CoZd Bay district, on the Alwh PeninsnIa, issue from two formitiom. In the vicinity of &Id Bay they come from the Sbebkof formaEion,8¶ which contttins bd~equivalent in time Oo at least part of the Chinitna shale, for they carry Ehe C&m huna The =pages on the Pearl Creek dome, west of the south end of Becharof Lakel come from beds of the Mh& formation, which caps the dome. The oil, hewevex, may originate in the Shelikof formation, below the Nhk,md thus mefrom practically the mehorizon as that in the seepages new Cold Bay. The relation of the oil seepages and wda to the geologic stractnre of the formation in which they occur must be considered in prtsdicthg the 10~~~0~1of a mble oil pool. The seepap .on XaiU Bay ie war a fault, rand the principal seepage at Oil Bay is in a zuna of jpinting rand faulting. The position of the easf and west shores of Oil Bay wag determind by a system of vertical faults and.cildy * ripad joints, which in generd strike N. 20" W. A glance at the geologic msp (pl, 2) shows clearly that the sapage md drill holes at Oil Bay are in Pine with the weshore of the bay and that unlw the fracturing dow not extend that far north the position of the: -page may readily have been controlled by the same causes that mntrolled the form md location of Oil Bay. The accumulation of oil, however, would be detern-i~~sd.byother conditions tbthwe, and in this locality it might be expected to depend primarily on the structure of the beds and the pmnce of rocks of proper character to contain and to retain the oil. In addition the quantity of oil in a given resemoir would ahdepend, in part, on the extant of the gathering ground or drainage area. The mks of a narrow curving belt dong the coast of Cook Met dip miward in B monocline that carrim them from view beneath the water. This structure includes the rocks above the Tnxedni smdstone as wall as that formation and is BO pmnounced that it suggested the name Tilted E'iUa for the mountaiins of the Mt, The Tuxedni sandstone of the interior and the northwd side of the peninsula has hen thrown into a succession of folds whom axes run &boutN. 30" E. The paition of these folds is indicat& on Plate 8, where it is shown that one of the two principal anticha follows the valleys of Wrand Fitz C;reeks. This anticline divides into two minor anticlines in the north end of the Pitz Creek Valley and flattens out toward the south end near Oil Bay, apparently losing its identitg beneath the southward-dipping beds of Mount Pomewg. Possibly them are minor folds on the enst 0dof this anticline htween Park Creek and the head of Brown Cd,but lack of time prevented a , car~fulexamination of this area. The other anticline, which extends through the Portage Ch& Vdey, is a closely compressed fold and is cut off on the north by , a fault that crossas its axis at an acute angle. It would morn that the anticline of &e Fih and Bowser Creek Valleys and the seaward- dipping beds along Cook InIet furnish struchml conditions that would favor the accumulation of oil, because the anticline and its broad &rn limb provide both a reservoir and a drainage area. The gtorage of oil in the rtnticline would necessarily depend further on the presence of beds capable of holding oil and on a capping of beds that would prevent its escape. One posbiblg unfavomble ht~mof the Bmmr-Fib Cmek anti- &@ should be pointed out. Fitz Chkhas cut its vdey deep into the Tbdni sandabne, so that the robexposled near ChiniBa Bay, laa indicated by the &om, are mmewhtat low= in the fomtion than the bib at Oil Bay. The lowest beds expad on Fitz thek may thns lia below the oiI-bmring beds and pospibly no oil will be fond in them Whether or not this b- tme can not be d&rmhBd till more ie horn ahtthe EK)~of the oil. - me valley of Portage Creek would seem to offer a 1- favorabla locality to teat for oil, busethe rocks are; so closely compw that the limbs of tbe nmwfold we almost pdeIin placas and * becaum the fold is ad&d by s profound fault, which cuts off its north end completely. Oil might be found in other stmctural features than the two folds ddymentioned. One such feature would consist of a Imticulnr bed of porous sanhne, capable of holding oil, hc1din a bed of shale tight enough to prevent the escape of the oil. Such beds may be premnt in the upper Bhely park of the Tuxedni sandstone, but their murrence at a particular Iocality couId not ordinarily be pre- $idad from surface indications and wuld be determined only by the m. A tilted ~~e bed cut off by a tight fault migbt dm provide a rewmoir capable of holdiag oil, but here win the &&ulty of finding it in an undeveloped field would usually be great. It seems evident to the writer athat if other drill hol~am put down in the mamh for oil in thie disk&, they should be located with reference to a stmcturaI featm of one or the other of the two principal types just ddbed. The antidine in the vallep of Fib and Bowm Creeks is in reality the crest of an 1-et;riaal fold of whhkhe monmbe dong the shorn of hkInlet is the mhrn bb. In at l& one place them is a mEnor fold between the cregt md the momhe, but in otber places no wch minor fol$ wsdl fonnd. If 00 in considerable qusbntiQ were moving up dong the beds of the mondne, in plws it would probably find its way past *r ' the line of dec&g dip into the om& of the anticline. T%a tilted

sedimentary beds bordering Cook lnE& would mrn to provide a ' good gathering ground for oil and mnditiom favombIe, for its mmmdation, but the prwnce of oil can not be predicted and can hardly be, debrmhd by any otber means than the drill.

The probabili* of obtaining oil from the dimen* beds between Chinib and Tuxadpi Bap appears ta be I- thsn from the same hmtions muth af Chinitna Bay. Although the Jurassic Ids in &e vicini* af hiskin Bay and Oil Bay are known to carry a certgim quantity of petroIeum, as is shown by oil smps and drilling, &a structure of these !beds in the vicinity of Tuxedni Bay is not espe- cidy favorable for the aoeumdation of oiI, for, so far as observa- tion has shown, the structural featurea commonly considered as favorable ok ZI- for the retention of oil within an oil reservoir e :am not well developed here. On the other hand, the sedimentmy kda themsslvea are seemingIy as favorable for the development of .the oil M the corresponding beds farther 9011th. Tbe petroleum of

C Jnisllrim and Oil Bays is believed to be derived from the lower part af the Tuxdni sandstone or possibly fmm some lower sedimeata and is &red in the porous beds of that formation. If the bwer beds of the Tuxedni sandstone in the vicinity of upper Tuxedni Bay have emr contnined oil it seems likely that much of the oil has escaped to the hlurfsce and been Post during the long bethat thesa upturned .hds have been exposed to erosion, yet they may possibly still con- ibh oil stored either in lenticular beds of sand surrounded by im- pemriwa shale or in hdcc of sand that are sealed by being faulted again& imperviwa shale. Xf the deeply burid part of the formation in tbe area nearer the inlet is oil bearing, it is unfavorable for drilling because of the great &hichess of oper1ying hds that must be penetrated in order to ' reach the oil. The depth of the drill hole would be not only the -thichess of tha beds bult nn added depth due to the tilt of the beds, which, however, in beds of low dip is not great. The maximum depth ta the top of the Tuxedni sandstone near the entrance to Tuxedni Harbor is at least 5,000 feet. Drilling in this vicinity would therefore smm unadkble unless much more favorable structural mndi- &ions should be dimved than are now known. 5 IRON

af wrrs near no& * A deposit rnagnmtita found the shore of the 6de of Rzxdni Bay near its head. This deposit was not examined by the writer but was described to him by the owner, Mr. Roy A. hhsel, of Anchor*. Apparently it cuts the volcanic rocks at a point not far distant from the contact of the granitic intrusive that is exposed about the upper end of Tuxedni Bay. A considerable Myof the iron oxide is in view ~t this plm and is not far distant from the dmp channel extending northwestward hmSnug Harbor toward the hesd of the bay. The bbility of the deposit will ba of impohntle if the davelopmmt of the propee is undertaken. 56 ~Km~APE~B~ The foIlowing 81~~1~of om from this lodB were hished by Mr. Tmchd:

dnavsis by Kansas CItg TdgLabor~tory, Kaaaas MQ, Yo., &toW 14,lWO: lAIwa on on------,,----,----,---,,-*-- a21 lWca (Ella)-1-,,,------"-----,--,,,,,----- 4.84 $lumina (&o~),,,------~,,--,-,,-,------1-20

Iron (FoO)------d---I----I----r,,,,,,,,,-,,, 88.89 Lime (GaO),,-,,,-,-,-,,------,-,-,-- 1.66 Magnesia (MgO) -- 1.12 Sulphur (8),,,,--,--,-,,,,,, ------,-- .6B Manganwe (~),,,,,,,--,------2.08 * Phosphortlsl (P) -.0& -1 iron 138 metal (Fe)-,------,-,,-----64. !&' Analmfa by Abbot A. Hanks, Han Franclm, GaZY., Pebru- am, 1921 : Blli~a,,,,,,,,,,,,,-,,------,------,-,----,,----- 2.80 Iron---,,,----,,,,,-,,------,-----,------W.82 Phospborrrll, --,,,-,,,--,-,,-,--,,,,,,--,----,,,,084 Sulphur,,,,,,,,,,-,,------,-,,,-,,~, .11 Awts by Bogardns Teat- Labornbrim, Sattle, Waeb, July 2B, 1016 : Qold----,------,,--," Ounce per Zotl, 0.01 Bit~er,,,,,,,,-,,-,------~----- Trace Copper,,,,,,-,,,,,,,,,----,-,,,----,-,per cent- -40

The pvdde@h of the Snug Barbor district (p. 69) have not given promiee of containing valuable gold plwm or deposits of other valuable minerals. 'Sb district, furthermore, has not furnished lode deposits of commercial value up to this time. The possibility exists, however, that fiituq prospecting may raved such lodes, as one metaUiferons deposit of some promise has jud been d€scriM. ? TJ3E SNUG HAKBOR DISTRICT9 ALASKA

- meSnug Barbor L used hare to designah the district on *e we& side of Cook Met extanding muthward from the north sida of TndBay to Wtna Bay. Snug Harbor is the 1-1 term for the waterway betwe~nGhisik Ialand and the mainland on &he wad and is the usual destination given for freight consigned to the ummq on the south end of Chiaik Idand. A topographic map of the Snug Harbor didrict as far south ag Red Glacier waa made by C. P. McKidey in 1920. At the same time a gologic map of the urea was made by Herbert Insley and the writer, In 1981 this work was mtinued southward so as to cover the north shore of ChMh Bay and join with the detailed topographic and geologic map of the hi&n-Chiaitna Peninsula, surveyed in th~tyear, which are d-rihd in the iirsk part of this report. The Snug Harbor district include the northward extension of the geologic formations exposed on the Inkkh-GhinibPenhula and ha&md attention ixs a Mbbsource of petrolenm. A descrip- dim of ih geology is accodmgly included in the present repart, hpther with topographic and geologic maps (pls. 8 and 4) of the whole area betwean "Suxedni and Iniskin Bays on a scale of 2 1: 960,000. The topographic and gmlogic surveys of the Snug Harbor di&ct in 1920 were made during unusually adverse weather, in addition to which much time md labor had to be given to the e problem of transportation in an unsettled country pcxlrly sdaptgd ta &8vd with pack animals. In oomquence the extent of the surveys was much 1- tbm had been anticipated. Although the areal and stmctmd geology of the district is here treated separately from that of the Inkkin-Chinibs district, where the work was done in a mom detailed way, it seems advisable to tomidm the pstmleum reaoumm in obnnedion with those of the southern am The con- dnai011%wgarding petroleum will therefore be found in the wrlier part of this report. (See pp. 54-55.) Lwdh ad cg~cr-The district here described includes Chisik Xdmd and a part of the mainland between Tuxedni and C?hinitna 67 58 &HUG WBOR DISTRICT Bays, which cornprim the eastern foothills of Mwnt It"mmm. The areal geology of approximately 800 square miles of mountainous c0untry.i~repmnted on Plate 4. This ares is mmwbt less than. the amn represmkl by the topographic map (pl. a). OutJim of geography.-The shore of Cook Inlet from the head' of Tuxedni Bay to the haad of Chinib Bay fmm s rude Bsrnicircle with Mount Ilirtmna (10,086 feet) near ita center. Frm t&s high peak the streams radiate to the sea, and the intervening ridges slope 3 to its shore. The upper reach of Iliamna are snow covered (pl, 11, B$ and supply ice to the numerous glaciers, which give rim to the larger streams. When vieved from the sea, the fmthills sur- rounding Iliamna appear less rugged than when seen in the oppdte .. direction, for the maward slopes are dip slopes, conforming to the bedding of the underlying rocks, and the steep scmps, which are due to erosion and faulting, are not in view. msik Island exhibits this eharachristic well, for its high& point is on the northwest end (pl. 11, A),it9 northwest face is abrupt, and ib mrfsoe sIopes @- ually with the beds to the southeast. The~strildng fat~~~of' abrupt dopes an the landward side of the mountains and more gentle dopea on the seaward side are dm cb-achrigtic of the mountains bordering Gmk Inlet between Inihand Chinjtna Bays. All the principal streslns between Tux@ and Chitna Baye m glacial streams and on warm summer days carry a large vduma of water, but the glaciers that supply the water extend so fltr down, the slopes of Mount Iliamna, whose wmmit is only about 17 milea from the coast at the most distant point, that wna of tka streams are long. Johnson Eiver and West Glacier Creek am the long& and carry the largest volume of water. Their waters am haavilp chmged with silt, and their grades &re su small that much of their load is dropped before it reaches the se& Johnson Ri~meepeciaUy has thus built up for itself a wide, flat dley floor, which ia poorly draind and in most places is difficult to crtlss with horw or even! on foot because of the soft ground. The shore of Cook Inlet himl IIimns Point to East Glacier Creek is a broad mampy flat, crossed rt by meandering stream8 and bordered by sand bars, which doubtlw have been built np in large part of the fins material depmited bp the glacial waters deamnding from Mount Iliamna. This diatrict ia without trails. All travel alangshora is by bosvt, and apparently there hag been no incentive sufficiently strong ts draw anyone away fmthe coast. Swampy ground and thick Wrs. make trnvel inland difficult, except in winter, m thab sbeven. the natives rarely go away from the shore. Spruce timber does not grow in the uieinity of Bmg Ha*, ax- qtin a few areas lib that at F&l Point adon Chiaik IT. P. c~oI.O~:lr\I ~l'lt3'EY Rl't,i,l;tl V ir'b PLATE 11

I.. \irll \ l 11.1 2\1\,2. 1111111 .ldrll\%ar\ Ill\ I,.II \llrrl I : 11Il.I.~~1ir1\ I,. I lh \l#rl"I'FI

'1-lrr pc~lkir Ifl.fl86 TwI. II~HIVII LY-II Ir~rl. SI-m rwnlr. Crnln \ltlrrnr Blit~tr~nnfit wvrrr~lpl~~ces

'I$and, but it grows along the coast from Johnson River to Wtna Bay. Cottanwood, on the okher hmd, is widely distributed and grows ta large size. Trees 3 and 4 feet thick may be seen on Bar Ed,and fine groves are numerow. Practically dl the country up .ta an altitude, of about 2,000 feet is covered with a Iuxurimt growth of dderg throngh which are scatted hers and them smdI parh of hegms~ The grass in mer,as in mod of the Cook Met .' region, grow rank and furnishes abundant forage for dock. A ea~eryon Snug Harbor, at the south end of Chisik Island. ia the only s&tSeinent in this part of Cook Inlet. A wharf facilitates

m the loa- and unloading of freight, but there is no businem aside from that of the cannery, and thera are no ecxx)mmodations for travelers excapt those furnished through the murky of the carney officid~. The cannery is closed in winter, and only the caretaker remeins Even the timbers are removed from the whmf, for the ice drifting back and forth through Snug &rhr ~mimaway the phgand ma.it necessary ta renew the wharf em& spring.

STRATICf BBPHY

The geologic investigations made by Martin md Stantan in Tnxdni Bey in 1904 are described in a report on the Uiamna region " published in 1912. A further report dealing particularly with the possible presence of oil in the district was prepared by Mrtrtint and &illmom mntly a brief statement of the results of the surveys con- ducted in 1920 was made by the wrik8 The geology of the Snug Warbr district diffara Iittle, except in detarls, from thst of the Iniskin-Chinitnrr Peninsuh me ~amefor- mations m pr-nt, and the same general type of stmcture, thomgh slightly hpler in some r- is ~leea Only a smdl amof + Tertiq rocks and rn area of granite are present in ddition to the formations of the southern distri& 7%~areal distribution of the geologic formations between Tuxedni and Chinitna, Bays is repre santed on Plate 4. This map also shows their di~tributionin the Inish-Chhitna Peninsula but on a smaller scale than that of Plate 2. The character and thiclmegs of them formations in the vicinity of Tnxedni Bay are set forth in the following tabb, which Is M in part on the work of Martin and Stanton:

4~ lMutln, Q. C., and Kata, F- J., A poko@c reean~ceof the nlrmnr -on, M:U. 8, WLSnrvey Btrll. 486, pp, 6W4, 1912. 'Murtln. U. C., Prellmiaary repart on petroleum la am&&:U. B, -1. Rum Bd. 118. pg, 42-65, 1021. 'Momt, B. R., C)wlogy of tbs vIdnitg of TUT&II Bay, COak Inlet: U. B. -1. 8wve~ hll. 722, pp. 14.41-147, 1021. mate-: Bsmd, grad, moraianl, and OWma- soUdated &wxita Dm?Ju-c : Nohek Ionm5fw: bewt Shd% sande2om. a*, -1tle M, and mglomernte,,------,,,,------En000 Obislk conglommte member; mkme em- glonaerate, of varlable thiclme~gcow predoml nantIy of well-round& granite pebbles in an aodealtlc tnfraceoua matrix-, 2W) Chinitna shale: Fairlg homogeneom marlne MU- mentnry formatiom, consiEttlng of wft Meand wbordinate nmonnts of mansstone and lime stone------,--,,------*------&800L%400 Middle Jnraarric: lCuxednI madstone; marine sedl- mentary formatton conarteting pmlomina~~tlyof sanddone bnt IncIudbg a lar~epMportion of able aad wbordinate conglomerate and limestone,- 1, = Middle or Lower Jnrnsslc: Granite, granodforite. and gnarb diorlte. Inwer JatasEtlc (7) : lava flown at bJT lam ID-- slvea The thicknm shown in the table are thm given by Marfin, except that the thickmeas of the Tuxedni sandstone is increased,

which he snggested might lm necessary, as the result of the later + investigation in this vickitg. Martin and Stantqn studied in detail and meamred with mch enre the excellent sections of Mmzoic rocks expo& on the &oms af Tnx&i Bay and Chisik Island and on Chinitus Bay. They alao made extensive collections of fossils, which were the basis for mpa- rating the beds into the formations given in the table. Insley and - the writer reexamined these sections in order to Eamiliari7~them- k aim with the character of the beds, but did not remare them. . 'They ware able, however, to make a considerable addition to the number of speciea of fossils from the ldQ. m The areal distribution of the formations given in the tsble, is in general as follows : The axis of the main range of mountains extad- ing north and south from Mount nismna is made up of granite or of granitic rocb, chiefly amygdsloidal basalt md volcsnic agglomerate, which intruded an older complex of val&c rocIrs. Tbm igneous roch are borded on the east by a mdwof Juresflic marine diments, fmm whieb they are saparated by a fault of great displacement and length. The sediments, which incIude five distinct formations strududy conformable to one another, dip mod- , > arately and at a fairly uniform angle toward COok Inlet. They thus form a series of long, narrow belts parallel to the main mountain DESCRIPTIVE QEOLOQP 61 rsage, with the oldest formation lying adjacent to the volcanic rocks and the yomgest disappearing beneath the waters of Cook Inlet on the east. Two of the formations, however, 'are developd only Idly, and oonsqnmtly are not shown in pkces on the geologic map. Approximately 9,000 feet of these Middb and Upper Jurtrssic diments, consisting chiefly of sandstone and shale but including many beds of conglomerate, are known to be present in the vicinity of Tuxedni Bay. They extend southward and form the Zniskin- Chinitria Peninsula, bat are not known on Cook Inlet north of Tuxedni Bay, althongh it wms probable that some of them may be present there. Wl#*F.R .JIlRARRLC I 3 =ROCK&

Lav8 flows, tuff, and asmciated intrusive rocks a1.e exposed abut the upper part of Tuxedni Bay. Thwe nxhfom the high mountsins north of Mount nliamna and the adjacent inlsnd foothills and ere separuted horn the shores of Cook Inlet by the youngei sedimentary Msdescribed below, except where arms of the inlet, such BS Tuxedni and Chinitna Bays. reach back to them. The head of Tuxedni Bay is surrounded by granitic rocks of a eon- sidersbla varietg, incInding firmite, granodiorite, end quartz diorite, which are part of the beckbone of the Chigmit Mountains and extend north and mnth from this vicinity. Both shorn of Tuxedni Bay east of the sma of granitic rocks are occupied by darker volcanic rocks, which appsrently are older than the granitic rocks and are intruaed by them. Thew rocks, as determined by Martin,' include quartz porphyry, augih andmite tuff, and quartz porphyry tuff. Farther mmth on Chinitna Bay olivine basalt and tuff are prasent. The volcanic rockq including the lava flows and tuff, apparently form a Mt, abut 4 rn 5 miles in width, emding southward for many milee along the eagt side of the granitic rocks previously mentioned. The; prominma of the granitic rocks of the high mountains is the rasult of differsntial srosion. AEthough the volcunit: rocks consist largely of tuff and material in which bedding might be expected, their stmcture was not studied, and the degree of foTding which they have undergone is not known. Presumably they show the affects of pmum much mom thsn the dimsnhrg beds on the &, from which thy am separated by a f sault of patlongitudinal extent and large displacement. The age of the wlcmic and intrusive rock is not accurately determined bat was hntativdy mgded by Martin6 as Lower

aMutta, a. C, and %ts, P: J, A mloglc ree~s~ceof the JUamru reglom. Alamh : U. B. -1. Bnmy Bdl. 486, p. Ill, l0!22. ' MatHa, (3. C., op. dt, p. 61. Jumsde(P). Mathera found no evidence in the hmishak Bny region to disprove Martin's tentative assignment of Lower JuWc age to the volcanic rocks. He &owed mmidistablp that the granitic rocks am intruded into tbe volwnic mks but could find no eviderm to prove that siUa of granodiorite in the Tnxedni sandstone are off- shoots from the main granite batholith, elthough he regards that concl~~sionas reasonable. With regard to the ap of the granitic rocks he mys: In dl. probability. the gradtic rut.k*.bi thta and tldJacent portions of thtt Ma- Penhvnla are the -It 02 several intruslwa, cloerelj asllochted in WLW but distrlbnted at Inh-mIs thmnffhant the Mwer and,Middle Jnurastr em.

The Tuedni mndstone expwd on Tuxedni Bay may be divided inh twa parts, which difler from mcb other lithologically but are characterized by the same fossils. "She lower part consists dominantly of sandstone and other coarse-grained frapeotaE rack, including grit and conglomerate. This part of the formation also contains sandy shde nnd a Little hestone. It is typically exposed in a practically continuous outcrop on the shm of Tuxedni Bay fmrn Fossil Poiat westward to the boundary of the volcanic mh. The character of the fragments that mmposa the lower part of the Tuxedni formation indicates that these coarser-grained beds were formed from material such as angular grab sf feldspar snd femmagnesim minerals derived horn a land mma made up in larp part of granitic rocks, which was being worn down mechanically more rrr~idljthan chemical dietintegration mdd destroy the dhbris, and that the conditions of sedimentation varied rapidly. A section of the Tuedni sandstone, which includ~the lower part from Fossil Point westward, was measured carefully by Martin md Stanton in 1904 and is reproduced here to show the variety of beds included and the changing conditionu of sedimentation.

Bed* of part of dha Twr~ednds~tonu # msth 8- of TQpdui Bw

8hnlg saniWm with %catterm3 fwlh I-, !Z%=fm- Feet %fa, #pkawmwm, Phvlbcwa#, and othem---- W Black sanddne wltb gmaU white angular grab---- 8 Hard gray sandatone~~,~~~,,-,~~~~~~--,,,,,,- 1 Black @andstonewith Jmeeramrrs amblgwa, Sl.efrbwwraa

d. B, 61.umphrissionm, 15phu#nnww olllaturnP and other ! im,----,------,,----,,,,,,-,,-,--,--"------9 Dark sbaEe-,------,,--,,-,,--,,,,,,,,--,--- S'

#Mather, E. F., Ybtral e~sourcee of tba Kammk Bay mw: U. R. Bull. 773, pp. lBCt65, 1B26. lk& Wft coam black sandstone with white gains------39 . ~~in$B.#@y3&&with B~lowmmaebb- Be- dtep, and other 18

grayc&ale ,------+------36 Band8 of mndstone and shale--,----,,------3354 - . Dark soft ~hlyrwk with mar~-grabs------10 Dark Iimestone with abundant fdls, HpWmCepoB dea, Pl.mmm~,and others,---,-,,---,,,------2-4 Dark 3 Dark eongIumerate rock (ark-) ,------7% Dark shale wIth conglomerate bands----,--,,----,,,-- 28 ;SandW~ne------~--.--,--~----~-- 1- @my hole------+------^--^-^----^^^- 15 %~an&tone,----,,------,--,------~------2 AJhale with wtterea fwlla-,,-,------=?4 Bandetone and ahale with BtpAIMOomro~mrIotb~1188, H. &h- mr&w 61pRamma cepoidee, Lytomas, PhvtZocwual and many ether fosaik------+------#%I SWe with concretbnary bands 10 . I Ooncmled by a fault------,----,,-+------, 100" Gray &ale with nnmerous mudstone and con&onarg banda and a few foasila, including @fephamcwmcf. @. ha- 100 Gmy $hale containing fandstone and conmetiomry bands,-- lS0 Cfray ~and&onewith I=-8 MsoMgutsa and a few other bf~dves---,,------+---~-----~----~~--~---. lXl Idmestone congloberate wlth clavdlata and andnlata Trig* nlas and other fm&a -,,,-,,---,-,,,-,,,, 1 amy sandrrtofle ------,--,-,--,---,-,,,,3% Wk-gray fos~Ifemnssandstone ------,,---,--,,- 1 Qmg -&one with many smltll fmndk------,--,----ll Fowmferous conghrnerate with BeFemntdea------,--- ,, 2 &&y sandstone with Iamwamw Wferand Mw ct 5, gima-,-,+---,,,-,,,--,,,*,-,---,,,--,------,,,-, 52 Wdy shale with a few t&lo fndurated fossfIifemn8 sandstone bandsl---,----,----,-----,-----,-----,--,--, 86 Indurated Iedgerr of ttrgiIIaceom a6~1dstone1 to 4 feet thick, altemathg witb mewhat thlc%er beas of clas (fwd- iferotrs) ------2- ---~,---~~~,~,~--,-~~-,--,,-~-----~26 #bale with abundant ammonite& Htgpbtwxau,. Hmpomnm, endothem-----~-~-~--~~~--,--~-,~~~---~,~~-~~ 20 Indurated ban& of mndstone In ledges 1 to 1% feet tuck, alterntttiug with thicker beds of shale ,,-,,,,-,,-,--,,,, 14 More OF lem wdy~hde, weathering yeIlowh------200 Bandstone w-lth day ernwith abundant I;dw cE &. g3g&m-,,----,----,,------d,------"-,d, 38 Bofter aandstone and &ale to base of -re, partly coverd by talus composed of sbale+------d- -100 1, me upper part of the Tuxedni sandstone consists dominantly of @y and brownish &ale and is indistinguishable lithologically from the overIying chin it.^ shale. It contains mamy sandy Ms,espeei- ally in its lower part. This part of the formation was nat recognized h the field as hlongbg to the Tuxedni sandstone, and it is %parated from the mnitna shale on the evidence of fossils Chat were deter- mihed after the field work was ended The boundary line btween the two formations as repmmnted an the map may thewfore be subject to some alteration. The Tuxedni sandstone is exposed on Tuxedni Bay and on the f upper part of Johnson River but has not been recognized on the north shore of Chinitna Bay. Only a part of the formation, if any, can be present there. The Chinitna shah apparentlp lies adjawnt to the volcsnic rmks in this vicinity, as is shown on the geologic & map, which indicates that the Tuxedni formation has kncut out by the pea$ fqlt previously mentioned. The thickness of the ';ruxedni sandstone bn Tnxedni Bay is horn only approximately. Martin and Stanton found a thicknm of 1,128 feet for that part of the formtion which-they mdTo this measurement must be added a considerable thickness of shale that forms the upper patt of the formation, which is not exposed in the locality studied by them. More than 1,000 feet of sedimentary rock, chiefly shale, on Bear Creek is known to lie above the beds measured by Martin and Stanton, mid the btul thickness of beds b- 10ngiq to the formation in the vicinitJr of Tuxedni Ray is probably not less than 3,000 feet. HOWmuch of the original formation has been cut out by the great fault on the mest can not be determined from the evidence at hand. The beds of the Tuxedni smddone on Tuxedni Bay strike N. 30" E.,psdd in a general way tn the coast fine of Cook Inlet. The dip undulates slightly, ranging from 15" to 25" E., and is highat on west side of the belt of sediments. A few open folds were seen, but except for them the easterly dip of the beds seems to be notably uni- k form and practically uninterrupted. The age of the flrrtedni sandstone is well establi~hed. Certain parts of the formation are highly fossiliferok and have fmmi~hed % large collections which give proof that the sediments were deposited in late Middle Jurassic time. Fossil Point, which has long been known for the abundance of its fwsils, furnished gome of the earliest collections of fwils made in Alaska. The large collections of Tux- edni fogsiln from Iniskin Bay made by Martin and Stanton in 1904 was extended by Insley and the writer in 1920, and the combined list of forms is here given : Apoxrhals? sp. Belemniten sp. m?ilp Cmna? sp. &tart@ rrp. Enmim~trp. dstarte? RP. .Grammatodon sp. andocwae? sp. hotorrrdk wp 3noceramna ambiguus mchwald. PmtocardkP sp. Inoceramen exlmius. Pteria sp. lnoceramna Inciter. Rhynchonelle sp Inmrnmna porrectua. Bphaeroceras sp. ct. 8. oblatnm (Whit- Ltma ma. eaves). Lba cf. L 8phammma 8p. d. 8. cepoM~eIWhlb I enres). Lytoms rmrlottensfs. Ontree ap. BphaeromRs 6p. P&?I Bp. I Sphaeriola? sp. Pecten sg. ; smooth form. Stepl~anocernacarlottenslm. Perisphinctes sp. Stephnnncern~cf. S. humpbrleaIaaurn. Pbylloceras sp. Ste11har1cnreraalogndurn. PInna sp. Ateyhanocerns rlchardsoni (Whlt- PlenroIsJra sp eavea, Plenromya ap.,a. Stcpbnnoceras sp Plenromya sp. b. Mgonla sp. d. T. damn1 Whilwvcs. Pfeuromya ~p.c. Trlgonia, two specIea belonging to 'he Plwromya, three 8pecles. iI Cl~vellatae~nd Undulatoe. PraeconZaS up. 1 Tarrltella'l BP. All these forms except three species were found in the vicinity of Fossil Point. A single mlbction of ten species from a small stream 5 milea south of Fossil Point yielded three forms, A~w?&RPsp., Phy7- p.,md Tadellat sp., which were not collected at Fos- sil Point. This collection is undoubtedly from a higher horizon in the Tuxedni sandatone than those of Fossil Point. The following list ahows the plank collecbd in the viciniQ of Taxedni Bay. The detarminatious were made by F. H. &owlton, and the numbers am the specimen numbers of the National Museum. 7465. Just soutbenat of the end of F&l Point, Tuzedni Bay: mgwlgterls sp. P Fragment 8tema md other iragmenb. 7- Jmt we~tof extreme end of mail Point. TnsednE Bay: Bsgenopteds g8pwrttana Zig~lo. Fleldenia? sp. TM. Fossll Point, Taxednt Bag: Pterophynnm rafmahaleme Morrla. Bagenopteris g8ppertlana Zlgna. B~~. 746'7. Two bandretl yacds sonth of FmiI Point, Tuxedni Bay: emagrnents of Sagenapterts. ptewmallp 5. gsppertiana, 74M. Two hundred ynrda muth of FosslE Point, Tnxednl Bay: Wagenopter~i gtippertlana? I-. Two hnndmi yards mouth of Fmil Wt. Taxedni B~T: Elagenopterls sp.? 7470. EYve m1Ies ~onthof Fowl1 Point, on Taxedot Bag: Bagenopterie g8ppertfana Hmo. Macrotaeniopteria callfornica Fontnine. Nilwnla .orIentaIIa Heer. CladophIebi~sp. Pagiophyllam? m. Fieldenla nordenMoldI Nathomt ? In commenting on theee mllectjom IbowIton sap: Thla mateflat, although mag pretty mgmentw, contains a nrrmhr oi.interestlng tuIt k1or1ga Ln trppes part of the Jnrasalc. 5 * * 'Tltem fs a epeelmen of #a'agenopb& In the lot mat in the mast Intereating gpecimen of this genw E have seen, It is a very lam mature leaf en8 bas much of the snriarie betwen the vehs covered wlth raw perm that appear to represent tbe fdt. The q%tematic gosltion of #agBMgt&a ban Iong bee& In doubt, wme placing it among the ferns and otbem In the Hrdropteridine near YarsClm. Thls speplrnen map help to settIe the qumtlon. T

ElffIWITWA BRALE 9 The Chinitm shale is a dark srgillrtceous shale of gray, black, or reddish color, which indudes mbordinate beds of sandstone and limestone and shows numerous lines of limy concretions, especially in its lower part. It. rests conformably on the upper shdy portion of the Tuxedni sandsbne, from which it is distinguished by its fossils rather than by differencesin Iithdagy, dthough the shde of the Tnxedni formation is in part sandy. Chinitna Bay is the type locality for this formation. The shale is well exposed on both sides of the bay and extends in a narrow belt northeastward to CAisik Idand, probsbly an unbroken belt between 1 and 2 miles wide, dthough the prmm of the shale between East Glacier Creek and Red Glacier was not determined. A mtion of the Chinitna shale on the north share of. Chinib Bay, measured by Martin and Stanton, is given on page 24. This section shows a thickness of beds amounting to 2,085 feet, but poseibly not all the formation is included, for the west boundmy of the formation on Chinitna Bay is believed to be a fault contact, and part of the beds may be lacking in the section. In general tha Chinitna shale hrts the same strike as the Tuxodni sandstone beneath ihbutN, 30° Em-but a slightly lower dip. Folds were not seen in the, Chinitna shale in the vicinity of TuxeRedni Bay, but everywhere the low easterly dip is maintained. F The Chinitna &ale occupies the base of the Upper Jurassic action of Cook Met. At one time it was regarded as forming the uppermost part of the Middle Jurwic, but further study of the f ossih led to the separation of the two formatiom as has been indicated. Fomih are abundant in the limy wncretions of the Iower part of the shdile but are much less common in the upper part. They were not collected hrn the C'hiaitna shale of Tuxedni Bay in 1920. The ~BhaIe of the type hdity on Chinitrbn Bay is characterized by an abundance of lawcephalopods, among which several wecia of C&m are mmt numemm. The f-ilg colleetad from the shale of Chinitna Bay sre @ven in the bt on pages 2840. The N&ek formation, like the Tuxedni mndstone, is sf heterogeneous composition and includes interbedded shah, sandstono, arkom, ahde9itic tuff, and conglomerate. These rocks, however, fall into tf o main divisions, of which the lower consists dominantly of shale but indudes tuE and arkose and the upper of sandstone. The total thickness of the formation in this district is more than 5,000 feet,. W A coarse massive conglomerate is present beneath the shale member of the Naknak formation in the vicinity of Snug Herbor, and because df it61 development on Chisik Island it ha9 been named the Chisik conglomerate. This eonglomernte is a deposit of variable character and is not developed in parts of the area. It 1ins above the Chinit.na c hale and is now regarded as the basal member of the Naknek formation. It includes several hundwd feet of coarse mngllomerate in dhich are beds of finer conglomerate and of ssndstone. In some places, as on the beach near the cannery in Snug Hark, it contains cobbles and bulders of granite and other granitic mlm inclosed in a matrix of finer waterworn material and angular £rag- ments, which wording to Martin is an andesitic tuff. It is we11 displayed on Chi~ikIsland, its type locality, where it forms a eon- 4icuous cliff along the west and north sides: and it mfs in wme- what poorer development on the south shore of T~txedniBay opposite the island. It is present also in the mountains south of Johnson River but was not seen on the shores of Chinitns Bay. Beds of pit and coarse sandstone at the base of the Naknek formation in plaw 'where tha Chisik conglomerda is not developed are believed to be 440 time equivalent of the conglomerate. The Chisik .condomerate is stmctumlIy conformable with both the underlying and the overlying formations and has shared with them the moderate folding to . vhich they were subjected. No fossils have been found in i4 but ' M it Iies beheen b& which are lrnown to k.of Upper Jura~sic - 'age it-alsu is assigned to the Upper Juramic. . Ths upper part of the Nhek formation in this dihict is a f massive lighbwlo~.~3sandstone which forms a strong contrast with tb dark undm1ying shale and which is prominent topographically humit is resistant to weathering. It is mnspicuous both because of its color and because of the cliffs that mark its wastern boundary. lThe Nhek fomakion is exposed in e belt averaging 4 or 5 miles in width dong the coast of Cook Inbt from Chi~lik Island ~LI Ghinitna Bay and as noted elmwhere continueg southward along the es$t side of the InisKn-Chinitns Peninsula and into the Alaska Peniamla. Throughout the distance fmm C&ik Idand to Iniskin Bay it dips eastward beneath the waters of Cook Met. In this area tb mistant light-colored sandstone has determined the position of gold, but it is difficult to prospect and little sttent-ion has beefibgiven to it. The beach depwits form a narrow border along the shore for the most part, but on the north side of Tuxedni Bay and north of Chinitna Bay they widen to a narrow coastal plain, n+hichin one place has a breadth of over 2 miles.

smwmum -f The structure of the sedimentary beds in the vicinity of Iixedni Bay has been indicated in the descriptions already given and is shown on khe wction on Plnte 4. These beds from the Tuxedni sand- y stone to the Nahek formation have a moderate easterly dip toward the shore of Cook Inlet and strike psrallel to the shore, about N. 30" E. A slight flattening of beds near the mast line is notid, far the average dip there is between 10" and Is", as cornpad with 20" or more at the upper end of Tuxedai Ray. The ~aritpof 1-1 variations in dip is not able. Folds am1 even short undnlations in the bed^ are uncommon, although the dense covering of alders on all the lower hill dopes obscures the strnct~~rein rnRnp places and possibly con- ceals folds that are pent. The degree ef foIding, however, incre~sestoward Chinitna Bay ttntl becomes pronounoed bt.ween Iniskin snd Chiitna Bays, as is shown in the description of the Iniskin-Chinitna Peninsula ( pp. dW5). Faults of mall displacement were observed at diffewnt places, but no great faults were seen within the area occupied by the di- rnentary rocks. It is probable, however, that the contact of the Tuxedni sandstone with the underlying volcanic rcrcks is a fault contact. Martin, from his study of the relations &ween the vol-

canic rocks, the Tuxedni sandstone, ~ndthe Chinitna shale on Chi- 1 nitna Bny, reached the conclu~ionthat the sedimentary beds am most _ probably separated from the votcmic rocks by a fmllt of considerable . vertical and longitucfins! extent, although he st~ggestedother pox- T sibIe explanations of the relations existing there. The more recent investigations in Cook Inlet have shown that this fault exisb and is one of the notable features of the structural geology of the district. - HTBTORXCAL AND ECONOMIC GEOLOQY The ,oreolog.ie history of Tuxedni Bay and its vicinity is the same rts that of the hiskin-Chinitna Peninsula, a few miles ta the south. This subject is treated in the earlier part of this report (pp. 45-47), Some conclursions and suggestions relating to the pibilities of prducing petroleum in the Snug Harbor district and a description ' of a deposit of magnetite near the head of Tnxedni Bray are given on pages 6.5-50. INDEX

paw .- holds on tlla pwlmula ...... R-8 Mertin, Q. C., oItd...-,----...--- Z?. 5142,lagsg Mether, R. F., uiM 62 Bay, ...... ,------, Chtdtrm mud Rsts at W ot. plnte Metals. ~beenwof .-..,-----.--.-.-.---.. M showing 11 ...... Mwnt Elennor, plata showing ,.. 10 Chl~tnnlde, od~hinltna Bny, mtme and ;*(aunt Ilinmna, phto mbowlng.....-,--..--- 58 tMckm of 66 ...... Miahroom rocka, owmnoe of.----.,--..... 32 on the Inkkin-Chlnttm Pealmnh. we and cnrrelntion of..- ...... -1 KOtnek i-tIon, age Bnd rnrrel&kIrnOf.. .. -2 dsmitlon of...... 46 riermlllon OL...... 4Hf natnm snd dlsldbation of ...... Q. 23-2il lmeouq rocks Intxudd in ...... 374.4 platea shov$nz...... I, la58 I1 l holow or ra47 LbIcknm end abmctare at...... %3,8W3l nnrure nnll aubdfvisioar of...-.. .8-10,81.874 CblslL mnglomemte member. dspxzltion of.. 44 plutcs ~hnwiw.....---.-...,...... 4,IO. b9 fatme ~ndthlckm 01 .---,._-.*10,31-3267 011. &t Petroleum. I hoin.. rd 011 Bny. plntss shoWng-...... -...../ 10 C&lk Islanrl, pllrta ahowlug ,W .------.----.mountains on e~stBide of, pkte 6bowIna- 10 Cmot Hm of the pdda.,.-----u--.L--..- 4 Cook Enlnt, rock of the wet %de of...... 0-11 Pwk CmtValley, ulaw mthIn. .,.....-, 4 and 4@ fkslnesa d th penlnsnla...... 5 Petrohm, erplwntim drlllllng for.--..- nMum ot...... 3M2 Pmltr, tmDd snd exbt 01...... M wc!nrmncaor ...... X-M Pi~ldwork, wtlEne nl...... -_..------5-I pmncm of, uea Tnx~InlRny ...... M56 Fish and pmm --...... &g =pa* 01...... -...... -,, ...*...... 48-48 Pltt Crwk VaIW, -flew enat aaross...... 4 Ports or call...... ?4 Mds En tb rwh...... hU4 Pamrind Ruit m the pml&g ...... 7-8 Fossdsprrscnt...... 13, 15-n.%cn, ~7,%I, 53-65 Roller or the pnbm& ..A------,-..--...-44 ~ph~dtbe~dh...... -1-8 Snup nnrbor dlstrlcl, msmphy ol.-----.-. 6bW Glecld action fn the Snag ITarbor dMd.-. €Ed !WtiQrIof 87-59 on tha Iniskin-Chlnlta Perrlnsu1~----. 47 attutlmph~of...... W'IO IIlstdcal pmlogg of tb~~ndn ...... 45-47 ~tn~rtiueof ...... M Spum,J. E., cited 41 bbkln Eag, plaw ahmlng ---..------4,11 .,.,.,,,,-,.-.--.------..--. Stmhn. 1'. W.. fossfls detwmined by --..-_.Wa0, Imtmdas mkn In tbe Tuiednl s~ndstone, XNO,8bS9,Wl. M+i laat- Of .-----.----.---.-.--.--2a lBRatbphy. cmtllna al...... elf Imo,-t of. nrar Tmxednl Bay h+.w ...... Btructure 01 thbabsd rroelra ...... 48-45 rmdc (r), ham, &, heaturn of.. 11-12, n1-62 Rwaya, earlier-...... 2-3 J-4 MLddlq &.~ptlon of.. l%!B,W Tsrtlary rucb in the Baw Enrh dMck. ,, Ow.Iwmnums, duuTiptioo 01 ...... 2.142 J-lc dlmentary rock 01 -4Iaslm,ow. natara and occurrenw of--..----- 81WDB rel~tiontubk of ...... Z Tlmber oi the Inlsklu-Chlnltm ma¶uIn and Bnug narhor dlatrlet, d&l- Randah& cht,voleanic mkx a*hin by- Ma butlon or, mnp showing 8 Knawltoll, F. E., cited...... 63 bdsot...... 7 ldladebarmhd by ..... 21,-4&.6Ene.s8 Rails In tho twnlnrmle 5-7 ktlmof the peui~lsol~...... Tnxednl satidstone, am and mmlatkm or...... ts%a Map,wl@c, oftheInL~klnBny-Baue Awh deWHw or ...... -..-...... rcl dlswd*-*-----*------Intrualvo rmh In .-.----.---.--.-.-..-..Zi gedogEe. 01 the Intslrla Bar-Chlnltna nature snd dlstrlbntlon or.-.--.. 9,l%l4,W mnjmula.--- .... ---d.---- In Wkd. plntes d~ow~n~...... 1411 s~~~~~butjW~t~b~------8 sn~m~loilln .-----,-.---,...+-.-~. 62-44 -ic. 01 the falskin Bay-Snug thfdmm rind of --..__..---..-.11-38 Rarba dlatrlct.. . In pocket. d the Inislrln BapCMnitna Mu- Vo1f~nlcrmk~, Lonw JmcC?). Isaturn S~I~U IQ pocket. ol...------.---.,-. ....-r 1-12 1-6 71 0