90 0. H. Hershey — Florencia Formation. 



fectly definable, there seems to be no other course than to leave 

 it under the head of incertce sedis, or to place it in an appendix 

 to the Rhinobatidce, or possibly the Myliobatidce. 



A knowledge of the remainder of the organization of so 

 ancient a fish could not fail to prove of exceptional interest. 

 Where one stratum or concretion is capable of preserving a 

 fragile structure like this, the chances are that more abundant 

 and more perfect material will eventually be forthcoming ; and 

 it is not without the hope of stimulating further research that 

 the present contribution is put forward. 



As it becomes necessary to designate the above described 

 individual by a special title, notwithstanding its imperfect con- 

 dition it is suggested that the name Tamiobatis be employed for 

 the genus, in allusion to its fancied resemblance to the body 

 of Tamias. Specifically it may be known as Tamiobatis 

 vetustits. 



Museum of Comparative Zoology, Cambridge, Mass. 



Art. XI. — The Florencia Formation / by Oscae H. 



Hershey. 



Introduction. — Great progress has been made during the 

 past decade in the study of American Quaternary deposits, and 

 the literature on the subject is already voluminous ; but the 

 field is so extensive that many portions of it remain practically 

 untouched. These obscure corners contain much of the evi- 

 dence which in the future must be relied on to dispose of many 

 of the unsolved problems now before the geologic public. It is 

 by a gradual accumulation of a vast body of facts that we will 

 finally be enabled to read the Quaternary history of America 

 with great accuracy. Hence, every addition to our knowledge 

 of the superficial geology of the continent, however trivial it 

 may appear at the time, possesses some value as increasing our 

 familiarity with the products of the era. On this account I 

 feel it justifiable in placing on record this description and defi- 

 nition of the formation whose designation forms the title of 

 this paper. 



Description. — The Florencia formation is distinctly differ- 

 entiated into two principal members. The lower is a moder- 

 ately coarse subangular gravel. It is largely local in origin, 

 in northwestern Illinois, Galena limestone constituting often as 



