A recent article in this periodical (1962, bd. 42, h. 3, pp. 223-238) attributes the Bogo Shale of the Trondheim region to the Middle Arenigian (extensus zone, pars, of Britain; 3bγ of the Oslo district) solely on the evidence of the dichograptid content (species of Dichograptus, Didymograptus, Isograptus, Phyllograptus and Tetragraptus) of the shale. The species listed, however, with the exception of Isograptus caduceus, HARRIS varr., have no value, individually or in association, when it is desired to achieve a degree of correlation as precise as that which has been claimed in this case.
A note on the age of the Bogo Shale.