Association of American Geologists and Naturalists. 257 



animals of the North American ocean ; for probably the greater num- 

 ber of species are still living there, as they have already been found 

 abundantly on the German coast of the North Sea. The geological 

 position of the strata must be determined by the order of superposi- 

 tion, the larger included organic remains, &c, as it cannot be decided 

 by means of the infusoria." 



In the same memoir, Ehrenberg acknowledges in terms of just 

 praise, the value of the careful researches of Prof. Bailey, gives lists 

 of the fossil infusoria from two deposits discovered by Dr. Charles T. 

 Jackson in Maine, and states that the knowledge of the microscopic 

 organisms of Massachusetts has been much extended by Prof. Hitch- 

 cock through the discovery of several deposits there, during his geo- 

 logical survey. All of these deposits are referred, I believe, by their 



discoverers, to the most modern epoch. 



POST PLEIOCENE PERIOD 



The later tertiary strata of this country, though existing in but cir- 

 cumscribed patches, possess much interest on account of the questions 



concernm 



portion of the globe has undergone in the level of its surface, and in 

 * temperature during the epochs next antecedent to the introduction 

 of the human race. Of these post pleiocene, or pleistocene deposits 

 as they have been called, several small areas have been described by 

 •fe Conrad. The principal ones are in St. Mary's County, Maryland, 

 tod on the Neuse River below Newbern in North Carolina. To the 

 ame period he also refers the numerous small beds of Ostrea Virgin- 

 *■«, which skirt the low margins of the islets and rivers in Delaware, 

 dryland, and Virginia, and by many people attributed to the agency 

 °f the aborigines. The deposit on the Potomac in St. Mary's County, 

 18 especially interesting for containing several southern species, one 

 111 Particular, an estuary shell, the Gnathodon cuneatus, now restricted 

 10 the warmer waters of the Gulf of Mexico. Mr. Conrad infers that 



the 



Myt #* 



ros «, with species now inhabiting our coast as far north as Massachu- 

 *te. indicates a climate at the period of the formation, equivalent to 

 lhat of Florida ; perhaps we should say, an aquatic climate. The 

 *>** of the change of temperature which banished these shells from 

 ** waters of our middle and southern Atlantic bays, connected as it 

 18 with some of the widest questions in our science, will, I doubt not, 

 receive hereafter from American geologists and naturalists, the atlen- 



