216 New York State Museum 



These continental seas were extensions of the great 

 oceans and several could occupy the continent at the 

 same time, each from a separate ocean. Just as today, 

 each ocean was characterized by its peculiar fauna and 

 flora, though certain types might occur in two or more 

 of the oceans. Each continental sea carried the fauna of 

 the ocean of which its waters were an extension. When 

 the continental seas remained distinct their faunas re- 

 mained more or less distinct, and when they became 

 confluent there was, rarely, a commingling of the faunas 

 carried by each. Commingling of faunas in this way 

 occurred only very seldom. There is no evidence of com- 

 mingling after the Ozarkian and the best instance of it 

 seems to be the Upper Ozarkian fauna. Apparently 

 intermingling of faunas of distinct origin came about 

 through occasional submergence of barriers in areas now 

 covered by the Atlantic and Pacific oceans. Sometimes 

 a continental sea might be more or less cut off from the 

 ocean from which it had its source and the fauna which 

 it carried, thus isolated, slowly became modified until a 

 distinct fauna was developed in the restricted area. With 

 the spreading of the seas again such a fauna might be- 

 come widely distributed, more or less cosmopolitan. 



The geosyncline belts or areas of depression were for 

 the most part long and comparatively narrow. Though 

 subsiding continuously they were not always covered by 

 the shallow continental extensions of the oceans; some- 

 times, in part at least, they were above water and the 

 deposits they received were of a continental nature. In 

 some cases they passed into the shallow continental seas 

 in a direction away from the oceans, or again they might 

 be narrow troughs or seaways bordered on both sides by 

 land masses. It was in these geosynclines that the thick- 



