PREFATORY NOTE. 



Bulleliii 'Eo. 4 completes Volume II of tlie series, for the year 187G* 

 That much new and valuable matter to science has been issued in the 

 two volumes will, I think, be admitted. Whether the Bulletin will be 

 continued hereafter will depend on circumstances which cannot now be 

 foreseeu. A third volume may be commenced during the coming winter 

 when the field-work of the Survey is closed for the season. I^beg to 

 convey my cordial thanks to the colUiborators of the Survey, who have 

 furnished most valuable articles 3 also, to Dr. A. C. Peale, for the prep- 

 aration of the index. 



F. V. HAYDEX, 



United States Geologist. 



