92 A CENTURY OF SCIENCE 



lain by and associated with pink granites. For the 

 oldest masses, essentially the granites, he proposed the 

 term Laurentian system (1853, 1863) and for the altered 

 and deformed strata, the name Huronian series (1857, 

 1863). Overlying these unconformably was a third 

 series, the copper-bearing rocks. Since his day a great 

 host of Canadian and American geologists have labored 

 over this, the most intricate of all geology, and now we 

 have the following tentative chronology (Schuchert and 

 Barrell, 38, 1, 1914) : 



Late Proterozoic era. 



Keweenawan, Animikian and Huronian periods. 

 Early Proterozoic era. 



Sudburian period or older Huronian. 

 Archeozoic era. 



Grenville series, etc. 

 Cosmic history. 



The Taconic System Resurrected. 



The Taconic system was first announced by Ebenezer 

 Emmons in 1841, and clearly defined in 1842. It started 

 the most bitter and most protracted discussion in the 

 annals of American geology. After Emmons 's subse- 

 quent publications had put the Taconic system through 

 three phases, Barrande of Bohemia in 1860-1863 shed a 

 great deal of new and correct light upon it, affirming in a 

 series of letters to Billings that the Taconic fossils are 

 like those of his Primordial system, or what we now call 

 the Middle Cambrian (31, 210, 1861, et seq.). 



In a series of articles published by S. W. Ford in the 

 Journal between 1871 and 1886, there was developed the 

 further new fact that in Rensselaer and Columbia coun- 

 ties, New York, the so-called Hudson Eiver group 

 abounds in "Primordial" fossils wholly unlike those of 

 the Potsdam, and which Ford later on spoke of as 

 belonging to "Lower Potsdam" time. 



James D. Dana entered the field of the Taconic area in 

 1871 and demonstrated that the system also abounds in 

 Ordovician fossiliferous formations. Then came the 

 far-reaching work of Charles D. Walcott, beginning in 

 1886, which showed that all through eastern New York 

 and into northern Vermont the Hudson Eiver group and 



