G SeJiuchert — Prc-Cambrian Nomenclature. 485 



middle one as Agnotozoic, the youngest remains without a 

 name. The writer will not embarrass the workers in this field 

 of geologic endeavor by proposing a new name for it, but will 

 remark that Proterozoic could be made use of for the youngest 

 era. It will be remembered that Agnotozoic and Proterozoic 

 are equal terms, but that the former has priority through 

 definition, and that both were applied to all the rocks between 

 the Archean and the Cambrian. Since it appears that this 

 long time is divided by a revolution and at least one major 

 unconformity, Lawson's " intergranitic" division could well be 

 agreed upon as the Agnotozoic era and the "post-granitic" 

 division as the Proterozoic era ; or the terms could be reversed 

 if they should be found to agree better with the definition of 

 Irving and with the actual field relations. 



From the quotations given it was seen that Eparchean was 

 applied by Irving to the same time as Agnotozoic and that we 

 may therefore write of Archean and Eparchean time. The 

 latter term conflicts somewhat with Lawson's Eparchean In- 

 terval, but the latter has a wholly different meaning. Law- 

 son is correct in insisting that we should, in our geological 

 time-tables, take account of the "intervals," the erosion inter- 

 vals when the geologic record is being removed, and emphasize 

 at least the major ones by giving them distinct names. His 

 method is to add as a prefix the Greek word epi (=upon or 

 after) to the name of the time previous to the erosion interval, 

 as Eparcheozoic, Epalgomian, and Epiproterozoic. So long as we 

 keep clearly in mind the fact that Irving's term is monomial 

 — Eparchean — and that Lawson's is binomial — Eparchean In- 

 terval — there need be no misunderstandings. In any event, 

 we must begin to name the breaks in the geologic succession. 



In conclusion the writer offers the following amended ter- 

 minology for pre-Cambrian time : 



Paleozoic Era. Basal series : Waucobian of Cambrian Period. 

 ( Epi-Proterozoic Interval. 



( Proterozoic Era. 



j Ep-Agnotozoic Interval and Algomian Revolution. 



( Agnotozoic Era. 



j Ep-Archeozoic Interval and Laurentian Revolution. 



( Archeozoic Era. 



The unrecoverable beginning of earth history. 



Cosmic history. 



