XIV INTRODUCTION. 



0. muscidosa, Hall, but smaller; a finely striated Strop! todonta, 

 having the form and general appearance of S. magnified, Hall, 

 but also of smaller size ; the same Strichlandiana so abundant 

 in the cherty beds below ; and fragments of one of those curious 

 types of Dalmania? for which Mr. Conrad proposed the generic 

 name Odontocephalus, but much larger than the well known 

 0. selenurus, from the Upper Helderberg limestone — being pro- 

 bably not less than six inches in length, when entire. The 

 presence in this bed of this type of Trilobites, and the coral 

 Pleurodictyum problematicum, which, according to M. de Ver- 

 neuil, occurs in Indiana associated with well known Cornif- 

 erous and Onondaga fossils, leads us very strongly to suspect 

 that it will be found to belong more properly to the Upper 

 Helderberg series, with which, as developed here, it also agrees 

 more nearly, in its lithological characters, than to the rocks 

 below; but as the associated Brachiopoda seem rather to indi- 

 cate relations to the underlying cherty beds, we have concluded 

 to place it provisionally as an upper stratum of the Oriskany, 

 until a larger number of species can be obtained from it for 

 study. 



Directly overlying the above mentioned sandstone, there is 

 to be seen, at various places in Union and some of the neigh- 

 boring counties, a light-grayish, very hard, semi-crystalline, 

 often sandy, massive limestone, sometimes passing into alterna- 

 ting beds of limestone and quartzose sandstone. The fossils 

 found in this formation are the following, viz : Very large, 

 exceedingly thin-jointed crinoid columns, Centtondla hecate, Bil- 

 lings; Spirifer acuminatus, Con. (=S. cultrijugatus, Roenier); 

 several undetermined Spirifers, greatly extended on the hinge 

 line ; S. fimbriatus, Conrad ? Atripa reticularis, Linn.; a small 

 Productus, like P. subaculeatus, Murchison, but apparently more 

 distinctly costated ; Platyceras dumosum, Conrad ; and another 

 species of the curious type of Trilobites, mentioned as occurring 

 in the sandstone beneath, but smaller and more nearly like the 



