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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 66 



was engaged chiefly in seeking evidence respecting the boundary Hne 

 between the Cambrian and Ozarkian systems. For this purpose 

 many of the outcrops of these rocks were visited, but the most 

 important evidence was found in the Upper Mississippi Valley and 

 in Missouri where the Upper Cambrian rocks are particularly well 

 displayed, and the succeeding deposits of the Ozarkian system are 

 more commonly fossiliferous than elsewhere. The relative abundance 

 of fossils in these areas permitted the actual boundary between the 

 two systems to be accurately determined after considerable study. 

 This boundary, when determined, was found to coincide with the 

 uneven plane (see fig. 42) formed at the junction of the deposits 



Fig. 42. — Contact between Cambrian (Jordan sandstone) and Ozarkian 

 (Oneota dolomite) two miles south of Boscobel, Wisconsin. The undulating 

 line of unconformity is distinctly visible. Photograph by Ulrich. 



laid down by the retreating Cambrian sea and by those formed by 

 the return of the waters in the succeeding Ozarkian time. During 

 the progress of these stratigraphic studies numerous collections of 

 fossils were secured for the Museum series, and incidentally the 

 investigations resulted in the proper placement of many fossils whose 

 stratigraphic position had hitherto been uncertain. 



In the latter part of the season Dr. Ulrich worked out the field 

 relations of some insufficiently located collections of Paleozoic fossils 

 made in southwest Virginia at various times in the past. The most 

 important result of these investigations is the proof that a large coral 



