WILLIAM B. DWIGHT. 101 
The additional complication of American origin arose 
from the proposal by Professor Emmons of the name 
Taconic for strata supposed by him to be pre-Potsdam. 
This name, though not so conceived by Professor Em- 
mons, would, nevertheless, be a synonym for the earlier 
names—Cambrian and Primordial—proposed by Sedg- 
wick and Barrande. It has been, and still is, a sad 
source of contention among American, and to some ex- 
tent, among European geologists. But it has been 
clearly proved that, as originally applied by Professor 
Emmons, it covered strata which are for the most part 
Lower Silurian. This title, therefore, only makes the 
former confusion ‘‘ worse confounded,’’ and it would 
better be entirely dropped from geological nomenclature.* 
Many geologists in the United States have come to pre- 
fer the title Cambrian for the fossiliferous strata from 
the Potsdam or equivalent groups down ; some would, 
however, for reasons which are certainly strong, include 
the Calciferous, as more allied to the Potsdam than to 
the strata of the Trenton period. It would appear that 
this use of the term Cambrian is the one which meets the 
approval of the United States Geological Survey. 
If this plan is adopted, the next question would be as 
to the proper subdivision of the Cambrian strata. Mr. 
C. D. Walcott, the field geologist of the United States 
Geological Survey who is the chief expert in the study 
of these lower rocks, has recently proposed, and pro- 
visionally adopted, the following classification : 
1. Upper Cambrian—Comprising the Potsdam Group, 
Tonto Group, &e. 
2. Middle Cambrian—The Paradoxides horizon. 
*For a full presentation of the history of the Taconic discussions 
and researches, see the able paper by Professor James D. Dana entitled 
* A Brief History of Taconic Ideas,” American Journal of Science, De- 
cember, 1888. 
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