BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 1, pp. 469-480. April 24, 1890 



SOME ADDITIONAL EVIDENCES BEARING ON THE INTER- 

 VAL BETWEEN THE GLACIAL EPOCHS. 



BY PRESIDENT T. C. CHAMBERLIN.* 



{Read before the Society December 26, 1889.) 



CONTENTS. 



Page. 



Limitation of the Statement 469 



The Evidence drawn from the Lower Mississippi 469 



The Evidence drawn from the Ohio and Allegheny Rivers 472 



The Evidence drawn from the Susquehanna 473 



The Evidence drawn from the Delaware 473 



Conclusion 474 



Discussion 474 



Limitation of the Statement. — Evidences bearing upon the interval between 

 the glacial epochs may be drawn from various parts of the glaciated field, 

 and from the various phenomena connected with glaciation. It is not, how- 

 ever, my purpose to make any approach to an exhaustive review of these 

 evidences, or even to touch upon the arguments that may be drawn from all 

 the several sources. I desire simply to bring to your attention certain 

 specific evidences that have an important bearing upon the length of the main 

 interglacial interval, and that lend themselves more readily than others to 

 intellectual estimation. The evidences that are especially additional to pre- 

 vious knowledge are drawn from the lower Mississippi valley ; but, in con- 

 nection with these, I shall briefly refer to evidences drawn from other val- 

 leys that fall into marked harmony with them. 



The Evidence drawn from the Lower Mississippi. — In the lower Mississippi 

 valley the sub-stratum consists of Tertiary deposits. Upon these there is a 

 thin stratum of gravel and sand, known heretofore quite widely as the 

 Orange Sand, although that term seems to have been applied to different 

 formations. This stratum has been very considerably misunderstood. It 

 does not contain, so far as critical investigation shows, any material that 



* The facts relative to the lower Mississippi region are drawn in large measure from the observa- 

 tions of my associate, Professor R. D. Salisbury. 



LXII— Bull. Gf.oi,. Soc. Am., Vol. 1, 1889. (469) 



