The Eozoic Rocks of North America. 85 



very distinct from those of the Montalban. The mica is often 

 darnourite or sericite, and gives rise to unctuous glossy schists 

 passing into argillites, which sometimes contain a feldspathic 

 admixture. The limestones of this series, often magnesian, are 

 crystalline and include statuary marbles and cipolinos. We find 

 in the schists, which are intercalated alike among the quartzite 

 and the limestones of this series, masses of serpentine and of 

 ophicalcite, and occasionally of chloritic and hornblendic minerals, 

 as well as siderite, magnetite and hematite, the iroo-oxyds being 

 often mingled with the quartzites. These last are sometimes 

 flexible and elastic, and the whole series much resembles the 

 Itacolumitic group of Brazil. It has a thickness in different parts 

 of North America of from 4,000 to 10,000 feet, and is found 

 lying unconformably alike upon the Laurentian, the Huronian 

 and the Montalban. There are found in the quartzites of this 

 series the impressions of Scolithus, and in the limestones other 

 undetermined forms. This is the Lower Taconic series of the 

 late Dr. Emmons, which we distinguish by the name of Taconian. 

 Some late writers have by mistake confounded it with the Upper 

 Taconic of the same author, a distinct group, which Emmons 

 declared to be the equivalent of the primordial (Cambrian) of 

 Barrande. The Taconian is widely spread in eastern North 

 America, and appears to be also represented around Lake Supe- 

 rior by what has been called the Animikie series. There is reason 

 to believe that, on account of certain lithological resemblances 

 between the Taconian and the Huronian, the two have been in 

 some localities confounded, and that portions which have been 

 called Huronian are really Taconian. The latter, the writer has 

 elsewhere compared with a great series of similar schists and 

 quartzites, including serpentine, anhydrite, dolomite and marbles, 

 greatly developed in northern Italy, where it overlies the younger 

 gneissic and mica-schists series, and has been by various observers 

 successsively referred to the mesozoic, the paleozoic and the eozoic 

 periods. 



It now remains to say something upon the relations of these 

 different crystalline eozoic series to the Cambrian which succeeds 

 them. Forty years since there were two schools among American 

 geologists. One of these schools admitted the existence, between 

 the ancient gneissoid rocks (subsequently named Laurentian and 



