112 TJic American Geologist. August, i898 
Rut to get back to some of the more essential facts of the 
matter: The two classifications are not based upon wholly 
different data, as might be inferred from the recent articles. 
The one scheme purports to be based entirely upon the in- 
fallible fossils; the other on the combined testimony of the 
paleontology, the stratigraphy, the lithology and general 
physical records of the province. The one considers historical 
geology in the narrower sense commonly given in the text- 
books; the other in the broader geological sense. The two do 
not differ very much in practical application ; and not so much 
but that they may be readily adjusted. 
If professor Williams has indeed proposed names that he 
has not yet defined it is no reflection on the essential features 
of his classification. It often happens that geological terms 
get into literature before it is understood perfectly just what 
they are intended to express. In the cases of the three names 
under consideration it has been known for several years that 
professor Williams has been at work on a monograph of the 
Mississippian faunas, in which the three distinctions will be 
clearly set forth. 
It may be concluded therefore, that the names Chouteau, 
Osage and Ste. Genevieve have not been used more widely for 
one reason before all others. Previous to their application as 
an episode or age title they had been clearly defined and ex- 
tensively adopted in other senses. Chouteau limestone had 
already been used by Swallow for one of the formations of the 
Mississippian series. It was clearly defined; and it is still a 
common and useful term. Osage has been already com- 
mented upon. Ste. Genevieve w^as one of Shumard's names 
for a distinct formation; and by him was well defined. It is 
bad practice to use such names in very different senses. It is 
confusing, to say the least, to perpetuate synonyms even 
though they are pet names. 
Recent faunal investigations seem to indicate the base of 
the Mississippian series to be the bottom of Swallow's Chou- 
teau limestone. In this case, when a time name is to be recog- 
nized, Chouteau by modification becomes available. Yet, 
curiously enough, Mr. Weller, in his late article discards this 
term — the only one of the three that could possibly stand un- 
der the laws of priority. 
