OSCILLATORY CHARACTER OF CONTINENTAL SEAS 369 



tion of fossils there is never any doubt as to its identity from Missouri 

 on to the head of Frobisher Bay, in Baffinland. 



Next "the late Black Kiver and early Trenton fauna" includes the 

 Kimmswick limestone fauna, which, though clearly not a Gulf of Mexico 

 fauna, is best developed in the middle stretch of the Mississippi Valley. 

 From here it extends eastward, around the southern side of the Nashville 

 island, into the Appalachian Valley, and westward, around the southern 

 border of Ozarkia, to Colorado, where it is recognized in the Fremont 

 limestone. In the Mississippi Valley it is unknown north of Missouri. 



The third, evidently younger, fauna overlaps the northern edge of the 

 Kimmswick in northeastern Missouri. This third fauna has its best 

 development in the Fusispira bed of the proposed Prosser limestone in 

 northern Iowa and southern Minnesota. It is not very typically devel- 

 oped in Oklahoma, and quite unknown in the far west; but in a north 

 direction it is known in Baffinland. East from Minnesota we find it well 

 developed, though perhaps occupying only a few inches of limestone, at 

 the base of the Trenton in northern Michigan, Ontario, Quebec, New 

 York, and northern New Jersey. In the Mohawk Valley, in New York, 

 the bed containing the fauna is very thin and only locally present. In 

 New Jersey it wedges out southwardly, with the rest of the Jacksonburg 

 limestone, toward the head of an old bay into which this formation ex- 

 tends from eastern New York. 



The fourth fauna included in the synthetized late Black Eiver and 

 early Trenton fauna differs greatly from the others in kind and deri- 

 vation. While the first and third doubtless invaded from the north 

 probably by way of Hudson Bay, and the second may have come from 

 the Pacific, this fourth assemblage is made up mainly of species that 

 must have invaded from the south or east. This is the Praspora simuJa- 

 trix and Mesotrypa quehecensis fauna, known from Quebec and Ontario 

 to middle Tennessee. It is well developed in the Wilmore formation 

 of Kentucky and also in the lower part of tlie Trenton limestone in New 

 York; but in the upper Mississippi Valley, in Oklahoma, in the far west, 

 and to the north of Ontario it is wholly unknown. 



Finally, it includes two other faunas, one observed at a few places 

 between Nevada and Alaska, which can not be exactly correlated with 

 any of the other four. Its age is indicated only in a general way as 

 late Black Eiver. The other, or sixth, is the Maclurina fauna of the 

 Galena dolomite. Whether a little older or younger than the fourth 

 or Wilmore fauna has not been decided. 



Now, each of these faunas contains species common to two or more, 

 but in each again the majority of the species is peculiar to its special 



