Rusophycus as an indication of early Cambrian age

An unexpected find of probable trilobite resting trails in the barren Hardeberga Sandstone sensu stricto draws attention to:— (i) the danger of using the absence of fossils as a means of correlation; (ii) the possibility put forward by Seilacher (1956) of using trace fossils for distinguishing between Cambrian and Eocambrian beds; (iii) the question of the age of the Hardeberga-Ringsaker Quartzite complex in Scandinavia. Rusophycus parallelum ichnosp. nov. is described.