I^RE-CAMBRIAN LIFE 57 



Colorado Canon in the Western United States, 

 Walcott has found a small roundish shell of uncer- 

 tain affinities/ 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. 



The Kewenian series of Lake Superior has 

 yielded no fossils, but the pipestone beds of Minne- 

 sota, supposed to be about the same age, have 

 afforded a small bivalve shell allied to Lingula ; ^ 

 and the black shales of the head of Lake Superior 

 contain some impressions supposed to be trails of 

 animals.^ 



It has been a question whether the beds above 

 referred to should be regarded as a downward con- 

 tinuation 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 Palaeozoic Period. Van 



* Discinoid or Patelloid. ^ Winchell. 



^ Selwyn and Matthew. 



