84 Upper Cretaceous Fauna from Tennessee [282 



At both the Owl Creek (Miss.) and Brightseat (Md.) lo- 

 calities the fossil beds occur directly below the Cretaceous- 

 Eocene contact. This contact represents a long interval of 

 erosion during which the shell beds were at, or very near, the 

 surface and were probably subjected to the action of circu- 

 lating meteoric waters which had a disintegrating effect on 

 the shells. The abundant springs at this horizon show that 

 during late Pleistocene and Eecent times this uncomformable 

 Cretaceous-Eocene contact has furnished an easy channel for 

 ground waters which have attacked the unpetrified shells. 

 At Coon Creek, on the other hand, the conditions are some- 

 what different. There is no overlying uncomformable contact 

 dircetly above the fossil beds but instead there is a great 

 thickness of overlying impervious Eipley clays. The shells 

 were sealed up by the Upper Cretaceous sea in compact, cal- 

 careous sandy sediments and have been, it seems unaffected 

 by circulating ground waters until the dawn of the present 

 physiographic conditions. Even now these beds are so imper- 

 vious that the ground water does not penetrate them, as is 

 shown by the fact that well-drillers have reported the strata 

 perfectly dry. The character of the matrix at the three locali- 

 ties is essentially the same, so that it seems reasonable to 

 assume that the Coon Creek shells are well preserved because 

 they have been protected from circulating ground waters the 

 action of which is so evident in most Cretaceous strata. 



OBSERVATIONS ON THE FAUNA 



The Coon Creek fauna is both prolific and varied. Four 

 days collecting at this locality yielded, according to preli- 

 minary determinations a fauna of 134 genera and 269 species, 

 and further collecting has materially increased this number. 

 The study is yet incomplete and some of the determinations 

 are merely tentative but the following generalizations may be 

 made. In the 134 genera already recognized there are, exclu- 

 sive of the Mollusca, three genera of Vertebrata of the Class 

 Pisces; 5 of Arthropoda of the Class Eucrustacea; 9 genera 



