THE APPEARANCE OF LIFE ON THE GLOBE 331 



they should have at last yielded some remains of 

 organisms to the investigations of the Geological 

 Survey of the United States. In the great canon 

 of the Rio Colorado, the finest and most magnifi- 

 cent of these great gashes in the Earth's crust, 

 Charles Walcott made known to us five years ago 

 the presence of colonies of Hydroids related to the 

 Stromatopores, who are Molluscs possessing a 

 conical shell (genus Chuaria) resembling the limpets 

 which cling to the rocks on our own shores, the 

 presence, perhaps, of pelagic Pteropods, and, 

 lastly, of a well characterized Trilobite ring, seem- 

 ingly akin to the Cambrian forms. 



Farther north, in Montana, the pre-Cambrian 

 series is locally designated by the name of the 

 Belt series, and comprises 3600 metres of schists, 

 quartzites, and limestone. At two different points, 

 at the entry to the Deep Creek Canon and 

 in that of Sawmills, traces of organisms have like- 

 wise been discovered, such as the tracks of Annelids 

 belonging to four different species and numerous 

 other tracks due to Molluscs or Crustacea. But 

 these layers contain, in addition, in immense quanti- 

 ties, the remains of one or several genera of large 

 sized Crustacea, deformed, flattened and generally 

 in fragments, of which the most characteristic 

 form has received the name of Beltina Danai, in 

 memory of the illustrious geologist Dana. It is no 

 longer possible to doubt the existence, in the pre- 

 Cambrian seas, of Molluscs, Trilobites, and Gigan- 

 tostraca, analogous to those which swarm in the 

 Cambrian and Silurian strata. 



What conclusions should be drawn from these 



