lO NEW YORK STATE MUSEUM 



nel widened and the sea transgressed Its western boundaries, carrying with 

 its sediments the later modified faunas over what had been the land. This 

 was the period of Oriskany sediment. Notwithstanding the opening aut 

 of this New York basin in its later history so closely are the faunas of the 

 Helderberg and Oriskany knit together that much of our evidence will be 

 found to bear as forcibly upon the latter as the former in all queries as to 

 the origin of the faunas and their distribution. 



Attention must also be directed to the fact that the Oriskany fauna, 

 after enduring for a time in this broadened basin till it had purged itself 

 of its Helderbergian elements, adds to itself forecasting elements of that 

 fauna which distinguishes the next succeeding geologic stage (Onondaga). 

 This phenomenon is not evident in New York but has been lucidly shown 

 to be the condition in the strata of western Ontario, in what have been 

 termed the Decewville beds. It is essential that we keep before us in the 

 interpretation of the eastern faunas this important fact that late stages of 

 the Oriskany fauna become commingled with the incoming migrants of the 

 next organic invasion. 



With these prolegomena we may let the summation of our theses wait 

 upon the adduction of the evidence. 



* * 



I have many acknowledgments to make for personal cooperation and 

 assistance in this work, often from sources least expected. These acknowl- 

 edgments are chiefly made in the course of the book but in some instances 

 we may follow the custom of the Greeks and not sacrifice to our heroes till 

 after sunset. 



