GEOGRAPHICAL DISTRIBUTION. 137 



great lakes enables the reader to perceive the relative positions of 

 these Azoic lands. There may have been other areas along the 

 Appalachians, and over the Rocky Mountain region, which future 

 study will bring to light. 



The Azoic regions laid down are — 



1. Canada north of the St. Lawrence, reaching northeast from 

 Lakes Huron and Superior to Labrador (C C), and the continuation 

 northwest (B B) to the Arctic Ocean. 



2. An isolated area in northern New York, — a peninsular pro- 

 longation, it may be considered, of the Canada region, — covering for 

 the most part Essex, Clinton, Franklin, St. Lawrence, Hamilton, 

 and Warren cos., and part of Saratoga, Fulton, Herkimer, Lewis, 

 and Jefferson cos. 



3. A similar area south of Lake Superior (S). 



4. West of the Mississippi, a small area in Missouri, in which the 

 famous Iron Mountains are situated ; the Black Hills in Dakota, 

 and the Laramie Range in Nebraska, as recently observed by Dr. 

 Hayden ; part of the Ozark Mountains in Arkansas. 



In northern New Jersey there are Azoic gneiss, limestone, and other crystalline 

 rocks containing great beds of the ore called Franklinite, analogous to the iron- 

 ore beds of northern New York: the lowest Silurian beds cover them un- 

 conformably. Professors Rogers have described the occurrence of Azoic rocks 

 in the Appalachians ; but, although probably occurring in the range, the evi- 

 dence is not yet conclusive that the rocks so designated antedate the Silurian. 

 Professor Safford mentions rocks of the Azoic age in eastern Tennessee, — a 

 part of the same mountains; but they are stated to be conformable, as far as yet 

 investigated, to the Silurian. 



The map of New York and Canada in the chapter on the Silu- 

 rian shows more precisely the form of the New York Azoic and 

 that north of the St. Lawrence. It represents also the Silurian 

 and Devonian strata of the State as they become successively the 

 surface-rocks on going from the Azoic southward. Adjoining the 

 Azoic (numbered 1) is the earliest Silurian, No. 2, which outcrops 

 where it is represented, but is supposed to underlie the strata num- 

 bered 3, 4, 5, etc. So No. 3 is the next formation which outcrops, 

 while it probably underlies all the beds 4, 5, etc. The Azoic is thus 

 the basement, and each successive stratum was a new deposit over 

 it in the seas that bordered at the time the Azoic dry land. 



In Europe the Azoic system has been distinctly recognized in 

 Norway and Sweden and in Bohemia underlying the Silurian 

 unconformable. The great iron-regions of Sweden are probably 

 of this age. In geological maps of other parts of the world 

 (and those of Europe and America are not always excepted) it is 



