684: Henry Shaler Williams. 



tion" (The Scope of Paleontology and its Value to Geol- 

 ogists, 1892). 



As the nature of the marine bottoms are shifted 

 geographically, due to filling, scour or crustal move- 

 ments, the faunas move with them, and if the environ- 

 ments are not otherwise changed, the species will go on 

 living without marked evolution. In this way the bulk 

 of the faunas in a given region may continue to live a 

 very long time by shifting with their special habitats, but 

 locally the assemblages are found to be restricted to 

 their facie s in a given formation. On the other hand, 

 migration is a very different organic movement, in that 

 new forms or migrants appear among native faunas, 

 having had their ancestral history elsewhere than in the 

 area into which they migrate. We are told that ' ' slight 

 mutations of the species take place wherever the fauna 

 as a whole shifts its place of habitation." Many new 

 species "are undoubtedly mutants of the species of the 

 previous dominant fauna" (Shifting of Faunas as a 

 Problem of Stratigraphic Geology, 1903). 



Professor Williams began to see in 1884 that at the 

 Cayuga Lake meridian the Devonian section "is Ham- 

 ilton, terminating with Tully limestone and Genesee 

 shale, then the Ithaca group, which has first a Portage 

 fauna, then the Ithaca fauna, third, the Portage fauna 

 again, and finally Chemung capped by Catskill and 

 Carboniferous. A little further east in the Chenango 

 valley, it is Hamilton ; then a fauna intermediate between 

 Hamilton and Ithaca (but no Tully or Genesee) ; then 

 the Oneonta, a brackish and fresh water fauna ; then the 

 late Ithaca fauna, still with Hamilton types in it; no 

 Portage fauna, but a Chemung fauna following the upper 

 Ithaca fauna" (Dual Nomenclature in Geological Classi- 

 fication, 1894). We therefore see that the actual sequence 

 of faunas in a given section is not "necessarily expres- 

 sive of biologic sequence" in the history of organisms 

 (On the Classification of the Upper Devonian, 1886). 



The Catskill formation, long thought to be younger 

 than the Chemung, Williams demonstrated to be contem- 

 poraneous with it. Early in his studies he said that the 

 Catskill deposits are "due to the encroachment of the 

 land and fresh water conditions upon the marine basin in 

 which the Chemung fauna flourished. The Chemung 

 faunas continued to live there so long as the marine con- 

 ditions were sufficiently pure to maintain their life, and I 



