The three collections of Lower Jurassic fossils from the Seldovia area duplicates material collected in 1904 by T.W. Stanton and adds nothing to the age determinations made previously. The presence of Wahneroceras (?) in your lot 51AGz21 and in lot 21242 plus the presence of Coroniceras in lot 2981 indicate the Sinemurian stage of the early Lower Jurassic. The corals from the Lower Jurassic beds have never been studied, although they are the northernmost Jurassic corals that have ever been found.

The ammonites from the "Difficult" member of the Tuxedni formation in the area between Chinitna Bay and Tuxedni Bay are identical specifically with the ammonites from the upper part of the "Difficult" member (formerly Lower Siltstone member) at the north end of the Iniskin Peninsula and from the highest beds of the Kialagvik formation at Wide Bay on the Alaskan Peninsula. The ammonites includ Emileia, Leptosphinctes, and Sonninia. The genus Leptosphinctes is represented by a coarsely ribbed species that is easily recognized and has not been found at a lower stratigraphic position in Alaska. As discussed in previously submitted memoranda, the ammonites from in the upper part of the "Difficult" member indicate a correlation with the lower part of the European zone of Otoites sauzei.

The ammonites characteristic of the Fitz Creek member are represented in your collections 51AGz136 to 138 from the tributary to Bear Creek south of Tuxedni Bay. Lot 51AGz136 contains two species of Stemmatoceras that are identical with species collected by Hartsock this past summer at his locality 51AHa10 near the head of Bear Creek. They are also identical with species collected on the south shore of Tuxedni Bay in unit 19 of the section measured by Martin and Stanton (see U.S.G.S. Bull. 776, p. 142). The Sonninia in lot 51AGz137 and the Chondroceras (Defonticeras) in lot 51AGz138 can be matched with specimens from the Fitz Creek member. Sonninia has not been found above the Fitz Creek member and Chondroceras not above the Cynthia Falls sandstone member. The ammonite genera present in the Fitz Creek member show that it corresponds with the upper part of the European zone of Otoites sauzei.

The fossils that you collected from the Bowser member represent two distinct assemblages. The lower assemblage, as represented in lots 50AGz140 and 141 is characterized by Sphaeroceras, Oxycerites, Leptosphinctes, Stephanoceras (Polyplectites) and Lissoceras. This assemblage is characteristic of the basal beds of the Bowser member on the Iniskin Peninsula. The presence of Sphaeroceras and Leptosphinctes indicates an age not younger than the parkisoni zone of the latest Bajocian. The other genera range up into the Bathonian but Polyplectites is not known above the basal zone.

The next overlying assemblage in the Bowser member is characterized by the Boreal scaphitoid genus Cranocephalites as represented in lots 51AGz142, 143, 115, 116 and 117. Your collections contain some unusually well preserved specimens of this genus. Also the position of some of your collections immediately above the collections containing the lower assemblage with Sphaeroceras, etc. shows that there is no space for a fauna of intermediate age. Furthermore, lot 51AGz115 contains two excellent specimens of perisphinctid ammonites and one specimen of Reineckeia. The perisphinctid ammonite belongs to the genus Planisphinctes which occurs in England in the zone of Zigzagiceras zigzag at the base of the Bathonian. Reineckeia is typically a Mediterranean genus, being rare as far north as central Europe and unknown still farther north. It ranges from the base of the Bathonian to the middle Callovian (zone of Zigzagiceras zigzag to Peltoceras athleta. The presence of these ammonites shows clearly that the beds in which they occur are not older than Bathonian. Furthermore, their stratigraphic position indicates that they represent only lower Bathonian.

There is still no faunal evidence for the presence of upper Bathonian or basal Callovian in the Cook Inlet area. I think that there has been sufficient collecting to discover faunas of that time interval if sediments of that time were present. Unconformities are frequently difficult to detect by physical criteria when similar kinds of sediment occur both above and below the unconformity. I hope that you will find evidence bearing on this particular problem when you do field work in the Matanuska Valley.

The ammonites from the Chinitna formation in the Tuxedni Bay area represent three distinct assemblages. The highest assemblage, as in your lots 51AGz26, 42, 44, 45, 46, 49, 50, 124, 125 and 126, is characterized by compressed forms of Cadoceras and by numerous Phylloceras. A middle assemblage, represented in your lots 51AGz52 to 58, is characterized by Pseudocadoceras and stout Cadoceras. The lower assemblage, represented by your lots 51AGz65 to 67, 73, 76 to 79, 145 and 146, is characterized by many specimens of Xenocephalites and Kheraiceras. These assemblages and their age relationships have been fully discussed in my paper on the "Callovian ammonites from Alaska," a copy of which is available in the office of the Alaskan Section or in my office.

The fossils from the Naknek formation belong to two stratigraphic levels. Your lot 51AGz123 contains species of Cardioceras typical of the basal few hundred feet of the Naknek. Lot 51AGz41 contains finely ribbed Aucellas that characterize the lower part of the Naknek above the beds containing Cardioceras.

The next overlying assemblage in the Bowser member is characterized by the Boreal scaphitoid genus Cranocephalites as represented in lots 51AGz142, 143, 115, 116 and 117. Your collections contain some unusually well preserved specimens of this genus. Also the position of some of your collections immediately above the collections containing the lower assemblage with Sphaeroceras, etc. shows that there is no space for a fauna of intermediate age. Furthermore, lot 51AGz115 contains two excellent specimens of perisphinctid ammonites and one specimen of Reineckeia. The perisphinctid ammonite belongs to the genus Planisphinctes which occurs in England in the zone of Zigzagiceras zigzag at the base of the Bathonian. Reineckeia is typically a Mediterranean genus, being rare as far north as central Europe and unknown still farther north. It ranges from the base of the Bathonian to the middle Callovian (zone of Zigzagiceras zigzag to Peltoceras athleta. The presence of these ammonites shows clearly that the beds in which they occur are not older than Bathonian. Furthermore, their stratigraphic position indicates that they represent only lower Bathonian.

The lowest fauna occupies an interval 400-750 feet thick immediately overlying the Twist Creek Siltstone. The interval is mainly siltstone, but contains several massive sandstone and conglomerate unit. Representatives of the fauna are present throughout from within 25 feet of the base to 50 feet to the top. This fauna includes Cranocephalites, Arctocephalites, Siemiradzkia, Cobbanites, and Parareineckia. The age of this fauna is somewhat in doubt, but Imlay (1962b) believes the evidence suggests a late Bathonian age for these fossils and further correlates them with the zones of Clydoniceras discus and Oppelia aspidoies. However, certain important elements characteristic of these zones are missing in the collections from this region, and it is therefore possible that this sequence of beds may be Callovian rather than Bathonian. (from Detterman and Hartsock, 1966, p. 40)