85 



While this long age continued, it not infrequently hap- 

 pened that trunks of trees, which grew on the land to the 

 northward, were carried out into the comparatively quiet 

 water, where, becoming water-logged, they finally sank, and 

 after a long time, were buried in the growing deposit of 

 shells. Eventually, however, this long limestone making 

 age came to a close, by the gradual shoaling of the water, 

 and the return of the mud-bearing currents. While at first 

 there were some oscillations in the region, mud deposits 

 alternating with deposits of shells, the conditions finally 

 became uniform, and for a long period of time the Genesee 

 mud-flats with their paucity of animal life, and their richness 

 of vegetable life, constituted the characteristic feature of this 

 portion of the Devonian sea. Of course subsidence of the 

 sea floor went on throughout this period, but it was a very 

 slow subsidence, so that the filling in by the fine mud, went 

 on at the same rate, the relative depth of the water remain- 

 ing the same. 



Not until the close of the Genesee age did the subsidence 

 become more rapid, and when this occurred, the deposits 

 became once more of a calcareous nature, giving rise to the 

 thirty feet of calcareous and concretion-bearing Cashaqua 

 or lower Naples shales. 



While these shales were being deposited, the water was 

 inhabited, amongst other animals, by Goniatites, the shells 

 of which are found in some of the concretionary layers. 

 These animals may have come to this American Interior 

 Devonian sea by immigration from the seas which then 

 covered Europe, or they may have arisen independently. 

 This latter is hardly conceivable, for parallelism of develop- 

 ment between America and Europe would probably not 

 have resulted in identity of species. As already noted, the 

 few members of the fauna in which Goniatites intumescens 

 and other Goniatites are the predominating species in this 

 region, mark only a westward extension of the fauna which 



