C. D. Walcott — The Taconic System of Emmons. 39 1 



the "Upper Taconic" in 1856, the name Taconic does not ap- 

 pear to have any place in the geologic' nomenclature of to-day. 

 The following tabulation of the successive phases of the 

 Taconic 'system viewed in the light of present facts is instruc- 

 tive. It was proposed in a letter from Professor Dana to the 

 writer : 



Phase I, 1842. 



" Taconic System " - True order begins. 



6. Stockbridge limestone.. II. Lower Silurian limestone. 



- j Magnesian slate of Graylock III. Hudson slate. 



/ Granular quartz I. Cambrian. 



4. Limestone II. Lower Silurian limestone. 



3. Magnesian slate of Taconic mountains III. Hudson slates. 



2. Sparry limestone II. Lower Silurian limestone. 



1. Taconic slate III. Hudson slates. 



Phase II, 1844. 



5. a. Black slate. Fossiliferous I. Cambrian. 



b. Taconic slate " Mostly Hudson slate. 



4. Sparry limestone II. Lower Silurian limestone. 



3. Magnesian slates., III. Hudson slates. 



2. Stockbridge limestone II. Lower Silurian limestone. 



1. Granular quartz I. Cambrian. 



Phase III, 1855. 

 I. Upper Taconic. 



2. Black slate. I. Cambrian. 



1. Taconic slate III. Mostly Hudson slate. 



II. Lower Taconic. 



3. Magnesian slate III. Hudson slate. 



2. Stockbridge limestone and Sparry lime- 



stone II. Lower Silurian limestone. 



1. Granular quartz I. Cambrian. 



Use of the name Cambrian. — There is no necessity for re- 

 viewing the Silurian- Cambrian controversy. All the facts, as 

 understood by many writers, are accessible to the student of 

 English geologic literature. It is my opinion that the name 

 Cambrian should be used for the system of strata characterized 

 by the " First Fauna." 



The Cambrian System was correctly established on a strati- 

 graphic basis in 1835, and included the same relative geologic 

 terranes as the " Taconic System," with the exception of going 

 a little lower in the section containing the Primordial fauna. 

 Like the Taconic, it included the Lower Silurian (Ordovician) 

 System, a fact noted and corrected by Dr. Emmons, for the 

 Cambrian, in 1842. The Cambrian section stands intact to- 

 day, and, on faunal evidence, separates into two great divisions, 

 the lower of which is the Cambrian System, as used by many 



* Made equivalent to the lower unfossiliferous part of Sedgwick's Cambrian as 

 known to Dr. Emmons at that time. 



