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PR Re EL Pe ee ee eS a ae ee eg ee 
of the Rocky Mountains. 77 
Primordial zone attains a considerable thickness in the southwest, 
and is charged with an interesting group of its peculiar fossil forms. 
The examination of others proved its existence all along the 
Atlantic coast extending westward from Canada to Wisconsin, 
Iowa and Minnesota, and thus a great period in the world’s geo- 
logical history formerly supposed to possess but a meagre fauna, 
the first representatives of life on our globe, has already yielded 
very abundant and varied forms. ‘The following is a summary 
of the principal facts and conclusions from our knowledge of the 
otsdam sandstone in the far West. 
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mining, nor can we hope to have where eruptive rocks seem to 
Predominate, As era have not known the Potsdam sand- 
d. except along mountains with a true granite 
_ 8. Wherever this rock occurs we are struck not only with the 
Singularity of the organic remains, but also with the remarkable 
uniformity in the nature of the sediments and the general litho- 
gical appearance, compared with its equivalents in more east- 
