CAMBRIAN FOSSILS FROM THE MOHAVE DESERT 



By CHARLES E. RESSER 



associate curator of stratigraphic paleontology, uxited states 

 national museum 



(With Three Plates) 



INTRODUCTION 



Twenty years ago Darton ' first announced the finding of Cambrian 

 rocks in Bristol Mountain (then called Iron Mountain), near Cadiz, 

 California, on the Santa Fe Railroad, about lOO miles east of Barstow, 

 a locality well south of any from which Cambrian fossils had pre- 

 viously been obtained. He pointed out the fact that these beds, which 

 rest unconformably on an eroded granite surface, dip down the slope 

 of the hills toward the east, mentioning, in his brief description of 

 the section, that the few fossil fragments found both in the shale 

 below the nodular blue limestone and in the limestone layers in the 

 shale above it. were thought by Dr. Walcott to be possibly Middle 

 Cambrian in age. A more thorough study of the region was made in 

 1921 by C. W. Clark, then a student at the University of California,' 

 who published a detailed description of the section, listing fossils from 

 two horizons. These lists, which had also been checked by Walcott, 

 included one new name among the fossils from the lower shale and 

 another for the single fossil found in the upper shale. Only the 

 latter was described sufficiently to preserve the name. The name, 

 Wanneria ? cadizensis, proposed for the new species in the lower 

 shale becomes a noinen niidiini. Clark's original collection, together 

 with one obtained later under the direction of Dr. J. C. Merriam, 

 is the basis for the following discussion of the contained faunas. 



]\Iy attention was called particularly to the interesting features of 

 these faunas while identifying the species prior to their return to the 

 University of California, the officials of which have very kindly given 

 their permission for the following descriptions. The types of the 



^ Darton, N. H., Discovery of Cambrian Rocks in Southeastern California. 

 Journ. Geol., Vol. 15, 1907, p. 470. 



' Clark, C. W., Lower and Middle Cambrian Formations of the Mohave 

 Desert. Univ. of Calif. Publ., Dep. Geol.. Vol. 13, No. i, 1921, pp. 1-7. 



Smithsonian Miscellaneous Collections, Vol. 81, No. 2 



