H. S. WilUams — Devonian System in N. America. 51 



varieties. On the other hand if the iron be in excess the result 

 is the various shades of green and blue. 



As regards fusibility, the lithia tourmalines which are free 

 from both iron and magnesia are infusible. The presence of 

 either or both of these elements brings with it a degree of fusi- 

 bility increasing with their increase till we find in those tourma- 

 lines containing much of either or both constituents easily fusible 

 minerals. 



The titanic oxide associated with the Hamburg and Dekalb 

 tourmaline attracted special attention because of its form. 

 Having been examined chemically it was studied microscopic- 

 ally by Mr. J. S. Diller, who observed as follows : " The small 

 iron black scales with a rather brilliant metallic luster are cleav- 

 able into very thin folia, the thinnest of which, under the 

 microscope, are perfectly opaque. In reflected light these 

 lamella? show three systems of cleavage planes, traces of which, 

 upon the plane of foliation, intersect at an angle of 60°. The 

 cleavage planes make a large angle with the plane of foliation 

 and it is evident that this mineral is rhombohedral in crystalli- 

 zation. It is infusible on very thin edges and does not become 

 magnetic when heated. By this means it is distinguished from 

 hematite and ilmenite. From its physical properties alone I 

 should conclude that it is a member of the ilmenite series rich 

 in oxide of titanium. As analysis shows it to be essentially 

 titanic oxide, it becomes of special interest. In the first place 

 it is the extreme member of the ilmenite series and in the 

 second place it is a new form of titanic oxide, which is thus 

 shown to be tetramorphic." 



Laboratory U. S. Geol. Survey, Washington, August 31, 1887. 



Aet. IV". — On the different types of the Devonian System in 

 North America ; by Henry S. Williams.* 



The sections of the Devonian rocks in North America pre- 

 sent at least four distinct types of stratigraphy in their out- 

 crops in different parts of the continent. The four areas blend 

 somewhat at their borders, but in their central sections are 

 very distinct. 



The four areas may be called the 



(1) Eastern Border Area, including the outcrops of Gaspe, 

 New Brunswick, Maine, and other places in Northern New 

 England ; 



* Read at the New York meeting of the American Association for the Advance- 

 ment of Science, August, 1887, and constituting a part of a preliminary report on 

 the Devonian to the American Committee of the International Congress of Geolo- 

 gists. 



