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rhick marine strata of Early Triassic age occur in eastern Idaho and adjacent areas. The area covered in this report lies along the eastern margin of an ancient miogeosycline. Basinward (west) the strata are thickest and consist of fossiliferous marine rocks with no red beds. Toward the craton (east) the strata thin and intertongue with red sandstones and shales. The Dinwoody and Thaynes formations attain their thickest marine development in the region of the Fort Hall Indian Reservation. To the east, north, and south of Fort Hall, the Dinwoody formation intertongues with the red Woodside and Chugwater formations; the T:Q.aynes formation tongues out eastward into the Ankareh and Chugwater formations. The zone of intertonguing for the Dinwoody formation follows a line from southwestern Montana along the Idaho-Wyoming boundary and turns sharply westward in northern Utah. East of this line red beds are predominant ; west of the line the red beds are absent or of minor thickness. A similar facies line for the Thaynes formation passes southward from the Idaho-Wyoming boundary through the 'Vasatch Mountains and does not turn westward in northern "'Ctah as for the Dinwoody formation. New ammonite faunas of Gyronitan and Flemingitan age are recorded from the Dinwoody formation. The Prohungarites zone, the youngest Scythian ammonite zone, is recognized in the upper part of the Thaynes formation. The post-Thaynes Triassic rocks of this area are of continental origin and are correlated with the Shinarump conglomerate and Chinle formation of the Colorado Plateau. The marine miogeosynclinal helt was destroyed at the end of Early Triassic time. The eastern Nevada geanticline (Nolan 1943) probably extended northward into Idaho in the middle and late Triassic.

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NAME CHANGES IN RELATION TO GROUP CATEGORIES SPECIFIC AND SUBSPECIFIC NAMESDetailed consideration of valid emendation of specific and subspecific names is unnecessary here because it is well underxu

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