30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 66 
was engaged chiefly in seeking evidence respecting the boundary line 
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 
Fic. 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 
