Recent necessary restriction of the stratigraphic span of the Cambric period to its original signification that is, with the trilobitic Paradexides zone as base, does not, fortunately, greatly disturb Iowa's Cambric classification, for the profound erosional conformity at the bottom may well be regarded, or not, as representing Early Cambric time. The Olenellus zone, or Early Cambric of Walcott, therefore, belongs not to the Paleozoic at all, but to the pre-Cambric, or rather Taconic period of the Proterozoic. Of course, Sedgwick's lowest Cambric strata, the Paradoxides-yielding horizon, rests upon old basement gneisses in the Wales region, with one of the most remarkable erosional breaks between nevertheless, the Paradoxides zone is Sedgwick's lower Cambric, the Olenus or Dicellocephalus zone, his middle Cambric, and Lapworth's Ordovicic his Upper Cambric. Compromise with overlapping Siluric of Murchison removes from the Sedgwick Cambric his Upper Cambric, leaving his Middle Cambric the Upper, or Late Cambric of our day, and his Lower Cambric our Middle Cambric, while we add a new Early Cambric.
Proceedings of the Iowa Academy of Science
©1936 Iowa Academy of Science, Inc.
"The Bearing of Cambric Re-Definition upon Iowa,"
Proceedings of the Iowa Academy of Science, 43(1), 249-250.
Available at: https://scholarworks.uni.edu/pias/vol43/iss1/66