EVOLUTION OF EARLY PALEOZOIC FAUNAS S3 



In the section loo miles to the south, at Resting Springs, Inyo 

 County, Cahfornia, a brachiopod closely related to Billingsella high- 

 landensis Walcott' occurs 2,800 feet below the upper limestone, in 

 association with the trilobite Holmia rowei. 



Comparing the species in the early Lower Cambrian fauna with the 

 Olenellus fauna, in strata 5,000 feet higher in the section, we find a 

 marked advance in the variety of the later fauna, but we do not know 

 how much of this may be due to the absence, from our collections, of 

 genera and species that may have existed during the deposition of the 

 earlier sediments. In the earlier fauna of the Waucoba section the class 

 characters of the Arthropoda, Alollusca, MoUuscoidea, Vermes, and 

 Coelenterata were developed, and while the study of the genera and 

 species adds a little more to our knowledge of the rate of convergence 

 backward in geologic time of the lines representing the evolution of 

 animal life, it, at the same time, proves that a very long time-interval 

 elapsed between the beginnings of life and the epoch represented by 

 the Olenellus fauna. ^ 



DISTRIBUTION OF THE LOWER CAMBRIAN (OLENELLUS) FAUNA OVER 



THE NORTH AMERICAN CONTINENTAL PLATFORM OF 



CAMBRIAN TIME 



The Olenellus fauna lived on the eastern and western sides of a 

 continent that rudely outlined, in its general configuration, the North 

 American continent of today. Strictly speaking the fauna did not live 

 upon the outer shore facing the ocean, but on the shores of interior 

 seas, sounds, straits, or lagoons that occupied the intervals between 

 the several land-masses that rose from the partly submerged conti- 

 nental platform east and west of the central continental area. On the 

 eastern side, the first land east of the central portion of the continent 

 extended from Alal^ama northeast along the line of the present Appa- 

 lachian range to and including the Green Mountains of Vermont. 

 Whether or not the fauna existed in the Connecticut River region to 

 the east of the Green Mountains is unknown. That it occurred 

 further east is shown by its presence in eastern Massachusetts and 

 northwestern Newfoundland. Its presence in a still more easterly 



1 Proc. U. S. National Museum, Vol. XXVIII, 1905, p. 237. 



2 Tenth Annual Report, U. S. Geol. Survey, 1891, p. 595. 



