184 H. S. WILLIAMS — SHIFTING OF FAUNAS 



scarcel}^ a single Hamilton species occurs above the Tally limestone or 

 the base of the Genesee. In the Chenango section and farther east 

 Hamilton species dominate up to the base of the Oneonta, and even after 

 it are frequent. In the Chenango section they appear occasionally in 

 the Ithaca group and recur (some of the more dominant species) after 

 the typical Chemung fauna has occupied the ground ; so some of the 

 Chemung species range upward as high as the base of the Clean con- 

 glomerate, at Glean, and to the top of the Tanners Hill section, at War- 

 ren ; to within 200 feet of the Sharon conglomerate, at Tidioute ; to 

 wdthin 100 feet of the Garland conglomerate, at Garland, lapping over 

 the place of Syringotheris by 100 feet and more in several of the sections 

 of this region, and in several places typical Spirifer disjunctus has been 

 found in abundance, associated with abundant specimens of Syringo- 

 theris, large and with fully developed syrinx. In the Meadville sec- 

 tions, however, the Chemung species have not been discovered higher 

 than the Riceville shales, above which the Waverly fauna comes in in 

 its purit}^ In Licking county, Syringotheris does not appear in the lower 

 Waverly faunas, according to Herrick, till the upper part of the Waverly 

 (above the Berea) is reached. Syringotheris is also absent from the lower 

 shaly part of the Knobstones of Indiana and Kentucky, according to 

 Doctor Kindle. All these facts are consistent with each other and with 

 the hypothesis that these three types of sediments were being deposited 

 within the same basin, at relatively the same distance from their source, 

 throughout the whole time represented by their sections, and that they 

 contained distinct faunas, which shifted westward with them with the 

 passage of time. 



Effect of Shifting on Species 



With the shifting the species which succeeded in holding the ground 

 of their original metropolis continued to live on without change, while 

 the new fauna was being developed in the newly occupied territory. 

 There were undoubtedly new species introduced by migration with each 

 succeeding stage of each class of faunas, but many of the new species are 

 undoubtedly mutants of the species of the last dominant fauna of the 

 previous stage. Slight mutations.of the species take place whenever the 

 fauna as a whole shifts its place of habitation. Thus, many of the 

 species of the Hamilton, which shifted westward to reappear above the 

 Genesee and lower Portage formations at Ithaca, are clearly mutants of 

 the Hamilton types, while those that occupy the same stratigraphic hori- 

 zon a hundred miles eastward, where the genetic succession of species 



