Association of American Geologists and Naturalists. 250 



cided in date with that formation, and this confirms, I think, my view 

 of their gradual disappearance. But it has been clearly shown that 

 contemporaneously with these very fossils, existed the Gnathodon and 

 other shells of the Mexican Gulf, indicative of a warm climate in the 

 so called post pleiocene period. Does this not suggest the conclusion, 

 that the expulsion southward of the Gnathodon and its tropical asso- 

 ciates, was unconnected with the northern drift and its assumed cold, 

 and occurred in all probability contemporaneously with the extinction 

 of the mastodon, at an era subsequent to that which witnessed the 

 strewing of the northern erratics. Whether the other cause I have 

 proposed, viz. the withdrawal from our immediate coast of the Gulf 

 m, that great tepid river in the ocean, could produce a sufficient 

 cooling of the climate of the adjacent continent and its coast, to effect 

 at length the extinction of the higher animals and the disappearance of 

 'he more susceptible testacea, is a suggestion which those will best be 

 e t0 weigh, who have studied the influences which that warm cur- 



' rem ote as it is, even now exerts in controlling the climate of the 



Lnited States.* 



Strea 



POST PLEIOCENE OF THE NORTH. 



T 



1 urning to the northern districts of the United States, we meet with 



°tner formation referable to the post pleiocene period, which is much 



more widely dispersed than that containing the Gnathodon, and which 



* lso sheds additional light on the epoch of the drift. This is the great 



e clay deposit which fringes so many of the rivers and lakes from the 



coast of Maine to Michigan, and from the parallel of the mouth of the 



ce this address was read, some very instructive facts connected with the 



Sin 



- «««» uuuicsn was reaci, some very jrisiruuiive iauta luiuic^icu ««m wo 



Ject °f the climate of the post pleiocene period, have been presented to the Asso- 

 ion by Dr. Amos Binney, as part of a valuable report on the land shells of 

 America. From this report, it appears that in Indiana and some of the ad- 

 w estern states, there exists a shallow deposit of clay, first noticed by Dr. 



Jfcent 

 



a s far 

 *arm 



l tat th 



en > ^hich abounds in fossil land shells. Among them a southern species of 



6ecina > n °w rare in the middle latitudes, occurs in the greatest profusion, being 



as tlle evidence of a single species can reach, an indication of a somewhat 



er temperature. But the value of this discovery is much enhanced by the fact, 



e same land mollusks underlie the remains of the mastodon and other large 



^alia at Big Bone Lick in Kentucky. Later than the deposition of the drift 



c "ley overlie, and earlier than the epoch of the extinction of the mastodon, 



re c H f ° S8llized lar »d shells promise when more fully investigated, to furnish a 



Beri^ ° f an intermedia te period, when according to the view of Dr. Binney, a 



tem * ° aIlow lake s existed in the West, and when, as we may conjecture, the 



era ! ratUre of lne region was at least as high as during the immediately succeeding 



oft he mastodon. 



