. Annual report of the Board of Regents of the Smithsonian Institution . 12,000 metres CD. URANIUM AND GEOLOGY JOLY. 375 tures. The radium of the Usernmulde is probably not very important,seeing that these sediments can not extend far doAvnward. The prin-cipal local source of heat appears located more especially beneath thesynclinal fold, for Stapffs table (loc. cit., p. 31) of the gradientsbeneath the plain of Andermatt shows a rising gradient to a pointabout 2,500 meters from the north entrance of the tunnel. It isobservable that the radio-activity of the granite increases as it ap-l^
. Annual report of the Board of Regents of the Smithsonian Institution . 12,000 metres CD. URANIUM AND GEOLOGY JOLY. 375 tures. The radium of the Usernmulde is probably not very important,seeing that these sediments can not extend far doAvnward. The prin-cipal local source of heat appears located more especially beneath thesynclinal fold, for Stapffs table (loc. cit., p. 31) of the gradientsbeneath the plain of Andermatt shows a rising gradient to a pointabout 2,500 meters from the north entrance of the tunnel. It isobservable that the radio-activity of the granite increases as it ap-l^roaches the Usernmulde and attains its maximum () where itdips beneath the syncline. The means of radium content in the several geological sections intowhich the course of the tunnel is divisible are as follows: Granite of Finsteraarhorn 7. 7 Usernmulde 4. 9 St. Gothard massif Tessinmulde 3. 4 The central section, however, if considered without reference togeological demarcations, Avould, as already observed, come out asbarely And this is the value of the radio-activity most near
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