Nature . rly indicated by a system ofcoloured spots—a plan worthy of imita-tion. The formations represented are LowerCambrian, Beekmantown shale withDictyonema and Clonagraptus, theHudson shale and Hudson schist (Ordo-virian = Trenton), and the SilurianRensselaer I irit = Oneida, Medina. Three crustal movements are recog-nised in the area :—(a) at the close ofthe Lower Cambrian, Upper and MiddleCambrian are missing; (b) the Taconicor Green Mountain movement whichfolded the Ordovician beds ; (c) a post-Devonian or Carboniferous movementwhich folded the Silurian Grit of theRensselaer Plateau. Mi
Nature . rly indicated by a system ofcoloured spots—a plan worthy of imita-tion. The formations represented are LowerCambrian, Beekmantown shale withDictyonema and Clonagraptus, theHudson shale and Hudson schist (Ordo-virian = Trenton), and the SilurianRensselaer I irit = Oneida, Medina. Three crustal movements are recog-nised in the area :—(a) at the close ofthe Lower Cambrian, Upper and MiddleCambrian are missing; (b) the Taconicor Green Mountain movement whichfolded the Ordovician beds ; (c) a post-Devonian or Carboniferous movementwhich folded the Silurian Grit of theRensselaer Plateau. Minor oscillationsare indicated by conglomerates which occur in the LowerCambrian, in the Hudson shale, and in the Rensselaer onlv ten years had elapsed since Cross andPenrose made a careful study of the Cripple Creek district,the people of Colorado asked for a re-survey on accountof the great development of underground working in theinterval ; this re-survev has been undertaken bv Fig. Canyon, Crooked River, Crook County, showing basalt of inner canyon intact with stratified beds of outer can) on. (Bulletin 252.) Lindgren and Ransome, who have now issued a report ofprogress (6) in advance of the laboratory examinations. The oldest rocks in the district are the muscovite andfibrolite schists; these are closely associated with fine-grained granitic gneiss. Both gneiss and schist are cutbv a reddish granite. A second type of granite is thecoarsely porphyritic Tikes Peak type. As a result of therecent work, the views of Cross upon the rocks erupted NO. 3/< NATURE [February 15, 1906 from the Cripple Creek volcanic centre are somewhatmodified ; the various rock types recognised by him areshown to be linked by intermediate forms; they are clearlyall divergent eruptive facies of one general magma,characterised by containing from 9 per cent, to 15 per cent,of potash and soda, the soda being always somewhat higherthan the potash ; no true andesite is recognis
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