394 C. D. Walcott — The Taconic System of Emmons. 



Art. XXXIII. — The Taconic System of Emmons, and the use of 

 the name Taconic in Geologic nomenclature ; by Chas. D. 

 Walcott, of the U. S. Geological Survey. With Plate III. 



(Continued from page 327.) 



Nomenclature. 



I. Use of the name Taconic. II. Use of the name Cambrian. 

 III. Classification of North American Cambrian rocks. 



Use of the name Taconic. — To the writer the evidence pre- 

 sented and referred to in the preceding pages proves that the 

 " Taconic System " was founded on errors of stratigraphy of 

 such character and. magnitude that the name Taconic has no 

 claim upon the geologist for recognition in geologic nomenclat- 

 ure. 



I endeavored to make, in 1886, an argument for the use of 

 the name Taconic for the Middle division of the Cambrian 

 System, but it failed in the light of later results of field work ; 

 and now I think that geologic nomenclature will be benefited 

 by dropping the name entirely. Based on error and miscon- 

 ception originally, and used in an erroneous manner since, it 

 serves only to confuse the mind of the student, when applied 

 to any formation or terrane. There are several reasons for the 

 foregoing conclusions that perhaps it is best to here state : 



1st. — The name is not applicable. The Taconic range, from 

 which the " Taconic System " was named, is not known to 

 contain a fossil of the First fauna or a formation that contains 

 one elsewhere. The " Upper Taconic " slates lie west of the 

 range, and the " Granular Quartz " series east of it ; and the 

 range is formed of strata of the Trenton -Hudson Terrane. 



2d. — The "Taconic System" was considered pre-Potsdam, 

 on two suppositions : (a) that the Calciferous sandrock of the 

 Lower Silurian is unconformably superjacent to the Taconic 

 slates, on the west ; (h) that the variation of the lithologic char- 

 acters of the Lower Taconic rocks, from the New York Lower 

 Silurian, indicates a distinct system of rocks. We find that 

 the unconformity (a) was based on errors of field observation, 

 and (b), that the "Lower Taconic" rocks are of Lower Silu- 

 rian age, with the exception of the lower quartzite, which is 

 Cambrian and. conformably subjacent to the Lower Silurian. 



3d. — The claim of priority of discovery of the Primordial 

 fauna is invalidated by the fact that the fossils found in the 

 Taconic slate were referred to a pre-Potsdam horizon on an 

 erroneous interpretation of the stratigraphy and not from com- 

 parison with a known fauna that had been stratigraphically lo- 

 cated in any clearly defined geologic section. 



