[Illustration: Fig. 13.--_Arenicolites (Spiroscolex) spirales_ (Billings) _and Aspidella tenanovica_ (Billings), _Signal Hill Series, Newfoundland._] [Illustration: Fig. 14.--_Fragment of Cryptozoon, Grand Cañon, Arizona._ Photograph from a specimen presented by Dr Walcott to the Peter Redpath Museum.] In a thick series of pre-Cambrian beds in the Colorado Cañon in the Western United States, Walcott has found a small roundish shell of uncertain affinities,[8] a species of Hyolithes, probably a swimming sea-snail or Pteropod, a small fragment which may possibly have belonged to a Trilobite, and some laminated forms which, if organic, are related to the Cryptozoon already mentioned (Fig. 14). [Footnote 8: Discinoid or Patelloid.] The Kewenian series of Lake Superior has yielded no fossils, but the pipestone beds of Minnesota, supposed to be about the same age, have afforded a small bivalve shell allied to Lingula;[9] and the black shales of the head of Lake Superior contain some impressions supposed to be trails of animals.[10] [Footnote 9: Winchell.] [Footnote 10: Selwyn and Matthew.] It has been a question whether the beds above referred to should be regarded as a downward continuation of the Cambrian, or as the upper part of an older system. Matthew, whose opinion on such a subject is of the highest authority, regards them as a distinct system, but as belonging, with the Cambrian, to the great Palæozoic Period. Van Hise, and some other United States authorities, would separate them even from the Palæozoic, and unite them with the underlying Huronian, as representing a "Proterozoic" or "Algonkian" Period. This is merely a matter of classification, necessarily more or less arbitrary; but I believe the facts to be stated subsequently show that it will be best to unite the Etcheminian and its equivalents with the Palæozoic, and to place the groups lower than this in one great division, equivalent to Palæozoic, and for which many years ago I proposed the name "Eozoic," or that of the Dawn of Life.