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The Oxfordian beds of the Jurassic upper Fernie group occur at many places in the Foothills and eastern Rocky Mountains between the International Boundary in the south and the Peace River country in the north. Their lower part (unit a) consists of glauconitic silt or sandstone and shale (Green beds), their upper part of dark shale with rusty weathering bands and concretions (unit bl) or dark shale with sandstone bands (unit cl=lower part of Passage beds). Unit bl is the northern equivalent of unit cl which is characteristic of the south. The Green beds are normally underlain by the lower Callovian Grey beds but locally they lie on the middle Bajocian Rock Creek member. They form an excellent horizon marker, both where they outcrop and in the subsurface. In the southern sections they are 50 to 60 feet thick. In the north (Rocky River sections) they consist of two glauconite beds, separated from each other by 50 to 60 feet of shale with concretions. These beds contain Cardioceratids of early Oxfordian age. Unit bl and the uppermost part of unit a in the south contain Buchia concentrica (Sowerby) which indicates a late Oxfordian or early Kimmeridgian age. In the western interior of the United States and in the southern plains of Canada the equivalent of the Oxfordian part of the Fernie group is the Swift formation. The Oxfordian beds of the Fernie group were deposited in the Logan Sea, which transgressed over parts of Western Canada after the late Callovian period of regression. The Canadian part of the Logan Sea was probably connected with the sea in British Columbia, and through it, with the Pacific Ocean. After the time of the late Oxfordian or early Kimmeridgian the sea began to retreat in the western interior of the United States, where the non-marine beds of the Morrison formation were deposited. During this time marine conditions still prevailed in the Canadian part of the former Logan Sea and there the final regression took place not earlier than in late Portlandian time.

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SummaryFrom the microscopic examination of lightly etched, cleaved (111) surfaces of banded blue fluorite (Blue John, from Castleton, Derbyshire) it is concluded that the coloured lamellae are not necessarily or exclusively associated with lattice-line imperfections. Elemental analyses, by electron dispersive methods, of fresh cleavage (111) surfaces in the immediate vicinity of small inclusions (c. 10 µm diameter) possessing associated coloured haloes detected no appreciable concentrations of impurities. From the evidence available, it is suggested that the zones of blue colour consist of colloidal calcium resulting from radiation damage caused by the intermittent deposition of radioactive material on the surfaces of fluorite during crystal development. The dispersion of colloidal calcium produced is particularly stable as a consequence of the close correspondence between lattice spacings in calcium fluoride and in calcium metal.