INSTITUTE OF SCIENCE, PHILADELPHIA. 217 



These results, however, do not justify the assumption of the non-exist- 

 ence of any transition beds between the Chesapeake and Lafayette groups. 

 Theoretically such beds must exist unless they have been destroyed by 

 erosion ; and in fact data pointing to their existence in North Carolina, and 

 possibly farther South, are in my possession, but are yet not sufficiently con- 

 clusive for publication. In view of the confusion which has hitherto existed, 

 it seems necessary to use caution and to await careful stratigraphical details 

 before proceeding to final conclusions. 



Washitigtojt, January 20, i8g2. 



ACKNOWLEDGMENTS. 



This work has been continued by the v/riter with the approval of Major 

 J. W. Powell, director of the United States Geological Survey, and to the 

 survey the writer has been indebted for the use of books and other facilities 

 during its preparation. 



To the Smithsonian Institution similar acknowledgments are due. 



Beside Mr. Joseph Willcox and Mr. Chas. W. Johnson, of the Wagner 

 Institute, a number of correspondents have kindly lent their aid in the collec- 

 tion of material or other assistance from time to time required. Of these, Dr. 

 J. C. Neal, formerly of Archer, Florida, and now of the Agricultural Experi- 

 ment Station, Oklahoma, and Mr. F. J. La Penotiere, of Tampa, Florida, 

 should be particularly mentioned. 



Mr. Geo. H. Eldridge, Mr. Jussen and Mr. G. D. Harris, of the United 

 States Geological Survey, have facilitated the work at various times ; and to 

 the officers of the Academy of Natural Sciences, especially Mr. Pilsbry 

 and Prof Heilprin, the writer is indebted for courtesies on several occasions, 

 for which he desires to express his sincere thanks. 



