n8 ANNALS NEW YORK ACADEMY OF SCIENCES 



Hovey, Prof. A. W. Grabau, W. M. Bowron, W. C. PhalcMi. Prof. .7. J. 

 Stevenson, Prof. C. P. Berkey, J. Bewley and H. V. Maxwell. 



The writer made use of slides loaned by Prof. ('. II. Smyth. Jr., in- 

 cluding those used as a basis for the sedimentary theory ; also slides loaned 

 by S. W. McCallie, State Geologist of Georgia, and a set of slides from 

 E. F. Burchard, of the United States (ieoiogical Survey. 



The field work was jjrovided for by a grant from the .lohii Strong 

 Newberry Fund of the New York Academy of Sciences. 



PART I. A STUDY AND CRITICISM OF PREVIOUS THEORIES 



ThK SlLliRlAN EkA 



Whether the events that took place during the Silurian era were such 

 as could give rise to immense deposits of iron ore pr('ci])itated as original 

 material and thus forming contemporary sedimentary iron ore beds, or 

 whether fossiliferous limestones and sandstones of a nature favorable for 

 the later penetration of iron-bearing solutions wo'c fornu'd during a por- 

 tion of this era, cannot probably be determined wit bout detailed study of 

 probable land and sea conditions at that time ; but if any extended study 

 of these deposits is to be made, a knowledge of land and sea areas and a 

 study of conditions that affected different kinds of deposits at the time 

 the inclosing strata were laid down seem not only desirable but iin])()rtant. 



According to Dana, the North American continent at this time con- 

 sisted of a broad land area extending from Alabanui nortliwai'd east of 

 the present Appalachian system through Georgia, Tennessee, the Vir- 

 ginias, Pennsylvania and into New York, there turning westward, skirt- 

 ing the Great Lake region, then turning in a more or less southerly direc- 

 tion through a portion of Wisconsin, then abruptly turning northward 

 and running far into Canada. The southern and eastern portions of this 

 continent must have extended far out into the Atlantic ocean. On the 

 west, was a fast closing sea area shut of^' from ihe cold waters of the 

 arctic regions by rather extensive areas of the An-hean shield. This left 

 an immense interior sea and a gulf or bay nearly 800 miles long, favor- 

 able to the presence of warm currents which undoubtedly greatly influ- 

 enced life in the waters and temperature conditions on the land. That 

 these conditions were responsible to a large extent for the texture, com]>o- 

 sition and distribution of the Silurian strata, we cannot doubt. 



Quoting from S. W. McCallie (216. p. 1G2) : 



"The region, however, of this tumultuous sea. with its i-apid. niovinc: cur- 

 rents, appeared to liave been rarely of long duration. Scarcely liad the deposits 



