THE ARCHEAN. 157 
Cambrian formed one of the large units of division, or one of sub- 
ordinate importance, was asked. But the opinions expressed by 
the various national committees on the use of these terms having 
been so various, it seems in order to consider the suggestion of 
Prof. Cope to abandon altogether the term " Group" as one 
of the classificatory divisions, and to substitute for it Realm ; 
leaving the word Group free for application to temporary and 
convenient collocations. Such a change would have many ad- 
vantages, will probably receive the support of many American 
Geologists, and perhaps will not encounter any serious opposition 
in the Congress. 
C. Give the horizons of non-conformability in the 
Arch E AN. 
The question of the number of planes of unconformability 
in the Archeau is really a part of the j)revious one, but was sepa- 
rated for greater clearness, and also because it does not follow that 
a physical break marks the beginning of a new System. 
Sir J. W. Dawson recognizes three breaks in the Eozoic (Pre- 
Cambrian) as follows: between the Upper Laurentian and Lower 
Huronian ; between the Lower and Upper Huronian ; and be- 
tween the Upper Huronian and Cambrian. 
Dr. T, Sterry Hunt recognizes a physical break at least 
between every two adjoining systems of his classification, and 
probably one in the Laurentian besides — seven in all, count- 
ing the latter and also one between the Taconian and the 
Cambrian. 
Prof. Roland D. Irving recognizes one between the Arch- 
ean (Laurentian) and the Agnotozoic; one between the Agnoto- 
zoic and the Cambrian ; and " minor, though still very exten- 
sive unconformities between the members of the Agnotozoic 
themselves." 
Prof. Joseph L. Le Conte accepts Irving's two grand 
unconformities in the Archean (Pre-Cambrian), but does not 
express an opinion as to the minor breaks. 
Prof. M. E. Wadsworth believes that non conforraabilities 
in the Archean thus far are petrological, not geological, and prove 
nothing concerning chronological division^ as they are local, not 
general. 
B 
