40 Introduction 



broken into the southwestern Onondaga of the Middle Devonian, is wholly 

 nnlike the eastern or Appalachian one. It is clearly linked with the 

 Brazilian Devonian sea, the faunas of which spread north by way of the 

 southern Pacific into the Gulf of Mexico, across Central America. Only 

 a few species are common to this southern and the Appalachian faunas, 

 these being cosmopolitan brachiopods. 



The Middle and Upper Devonian Maps (Plates VIII, IX, and X). — 

 The extension of the late Oriskany seas was continued into the Onon- 

 daga, the southern enibayment spreading most rapidly over featureless 

 America, along the western side of the Cincinnati Axis. When these 

 southern waters reached Ontario and northeastern Ohio, they met those 

 of the Xorth Atlantic, and the faunas of the two areas are found mingled 

 at the base of the Onondaga, in western Xew York, Ontario, and the 

 James Bay region. With these warmer waters appeared a horde of reef- 

 making corals, their best development occurring at Louisville, Kentucky; 

 Columbus, Ohio; in western Xew York, and across the Niagara River in 

 Ontario; north far less abundantly in James Bay, and east in the Con- 

 necticut trough as far north as Lake Memphremagog. 



The Onondaga submergence was conlinued, and in the Marcellus stage 

 of the Middle Devonian the southern waters spread across the medial 

 region of the Cincinnati Axis in Kentucky into the southern Appalachian 

 trough, and thus again united with the X"ew York Basin.' In the eastern 

 area, the sea was turbid, depositing in the main black carbonaceous muds, 

 with a meager fauna of Atlantic derivation. The mountain ranges of 

 Acadia had been rejuvenated through elevation, and the rivers flowing 

 from this land dumped their heavy loads into the northern portion of the 

 Appalachian Sea. In northeastern Pennsylvania the coarse detrital de- 

 posits of the Middle and Upper Devonian are about 10,000 feet thick aiid 

 m Maryland the series is not much less in thickness, but farther south in 

 the Virginias the strata thin out rapidly. To the north in eastern Xew 

 York this series also decreases in thickness, most of the Catskill Mountains, 



' Since the map of Onondaga time, pi. vlli, was made, Kindle has shown that 

 the later Onondaga sea was present in western Maryland, and that the 

 Appalachian trough was invaded somewhat earlier than Marcellus time. 



