94 Wisconsin Academy of Sciences, Arts, and Letters. 
rows—have so far been observed. The overlying basal sandstone 
of the Franconia, however, only rarely fails to reward a few min¬ 
utes’ use of the hammer with indubitable evidence of the presence 
of such remains. The most abundant and characteristic of these 
are the nearly hemispheric cephalic shields of several species of a 
new genus of trilobites, one of which was long ago described by 
Whitfield under the name Arionellus convexiis. As this trilobite 
does not belong to either Arionellus or any other previously estab¬ 
lished genus it is proposed to change its designation to Camaraspis 
convexus (Whitfield) Ulrich and Resser. 
Physical Evidence of the Breaks Between the Paleozoic 
Systems in Wisconsin 
General discussion .—In Wisconsin, as indeed is the rule else- 
v/here on our own and other continents, the physical evidence in¬ 
dicating long interruptions of the process of marine sedimentation 
consists mainly of phenomena of stratigraphic overlap. By careful 
comparison of the fossil contents of the successive beds and the 
identification of the fossiliferous zones in other regions we finally 
arrive at a fairly reliable conception of which stages of the com¬ 
posite geological time scale are represented by marine deposits in 
a given area and which are not. The most striking and important 
of the conclusions thus arrived at is that within the always rela¬ 
tively flat interior areas of the continents submergence by marine 
waters and the consequent marine depositional record is greatly 
inferior in volume of deposits and ages represented by these de¬ 
posits than in the submarginal Appalachian, Ouachita and Cordil- 
leran geosynclines. The structure of the latter regions with their 
long troughs and broader surface depressions naturally permitted 
more frequent and longer-enduring submergences than could have 
obtained within the more extensive, relatively stable and hence 
much less folded interior areas. But we must not overlook the fact 
that even in these submarginal troughs the stratigraphic record 
of geologic events is far from complete. In these also the record 
is broken at the usual horizons. Indeed, and despite the fact that 
the record in these troughs is more complete—or rather less inter¬ 
rupted, the stratigraphic planes at which conclusive evidence of 
retreat of the seas and emergence of the troughs is found are 
only much more numerous and each no less clearly indicated than 
in the geologic sections of the flatter interior areas. Consequently 
