466 A. AV. GRABAU THE SHERBVRXE SAXOSTOXE 



been entirely removed by the long post-Paleozoic erosion. The Tully sea 

 was limited on the sonthwest by lowlands bordered by stagnant pools, in 

 wliich the fauna became dwarfed. This produced the well known pyrite 

 layer of the Tully. which can be traced from the Genesee River to Erie 

 County. The fossils in this layer are on the average only one-fifth the 

 size of the normal Tully or Hamilton species. On the east the Tully Sea 

 was limited by the Sherburne Bar, and on the south by the encroaching 

 estuarine muds of the Genesee, which progressively overlapped the Tully 

 northward. (See the map on page 955 of volume .28 of the Bulletin of 

 the Geological Society of America.) 



The Tully fauna inaugurated the local modification of that remnant 

 of the Hamilton faima which was isolated by the formation of the Sher- 

 burne Bar and the elevation which cut off the Traverse fauna from the 

 west. Xot all forms became modified at first, since the condition of 

 deposition and the facies of the sea bottom remained favorable; but we 

 can trace the slow modification of this fauna into the Ithaca fauna, which 

 developed imder the influence of complete isolation and separation from 

 the center of migration of the Hamilton fauna. Subsequently, indeed, 

 this fauna became an integral part of the highest Devonic or Chemung 

 fauna, as was long ago pointed out by Dr. J. ^I. Clarke. 



The Sherburne sandstone, which succeeds the Tully in the Ithaca 

 region and westward, carries chiefly this modified fauna, though 36 per 

 cent of the species still represent Hamilton types. The descendants of 

 the lowan fauna likewise continue into the Sherburne and even the Ithaca 

 periods. TVith the close of the Tully deposition, however, the pelagic 

 Xaples fauna entered the Xew York province and continued during the 

 whole of Portage time in the more westerly area. This fauna could only 

 have entered the Xew York province from the north, where, in the 

 Petchoraland, on the other side of the Xorth Polar region, it is Likewise 

 found. It could not have reached Xew York from the northwest, as there 

 the very different Upper Devonic lowan fauna existed, some members of 

 which entered the Xew York province, as we have seen, at the beginning 

 of Upper Devonic time, and remained as a part of the Tully and the 

 succeeding Ithaca fauna.* The lowan fauna came again into the Xew 

 York area, and in greater force, at the end of Portage time, where 

 we find it well developed in the limestone lentils of the High Point 

 sandstone of central Xew York, as described by Clarke. The Xaple^ 

 fauna could not have entered the Xew York provmce from the 

 east, for there the Sherburne barrier for a time shut out all im- 



* Kindle has recently reported the Naples fauna from the Mackenzie River region, 

 which indicates a westward spreading of this fauna in late Upper Devonic time. 



