342 C. D. WALCOTT — THE TERM "HUDSON RIVER GROUP." 



Falls and beneath the red or variegated sandstone of Niagara river. He used 

 the same nomenclature in his annual reports for 1838 and 1840 ; and in a table 

 showing the classification of the New York rocks, published in 1*40,* he 

 used nearly the same scheme of classification except to place the Hudson 

 slate, characterized by graptolites, beneath the Calciferous and Potsdam 

 sandstones, thus anticipating the view subsequently published by Emmons, 

 and in part adopted by Logan and followed by Hall in 1862. By priority 

 of publication and completeness of definition, Conrad's term should have 

 been accepted and used instead of Hudson River or Lorraine. Why it was 

 not adopted by the New York state geologists remains unexplained. 



In proposing and defining the term Nashville group,f Professor J. M. 

 SafFord stated that the line of demarkation between the Trenton limestone 

 and the Hudson River rocks above was not clearly defined, owing to several 

 species of the fossils of the Trenton running nearly to the top of the Hudson 

 River rocks, and those of the Hudson River rocks extending down nearly to 

 the base of the Trenton. In his table, the Nashville group is made to in- 

 clude the Hudson River and Dtica slates, and the central and upper portions 

 of the Trenton limestone. This view was republished in the first biennial 

 report of the State survey in 1856. In the final report the classification 

 was reviewed;^ all the Trenton beds were united under the term Trenton ; 

 and the Orthis bed was considered as the base of the Nashville formation on 

 account of carrying the very characteristic species, Ambonychia radiata and 

 Oyrtolitea ornotus, also, Rhyuchonella modesta and 11, capax. Professor 

 SafFord .says: 



" On such grounds we make the bed in question Hudson River, and lix the equiva- 

 lency of the entire Nashville formation." 



The Nashville formation is assigned a thickness of about 450 t'v^t, and it 

 ig delimited below by the Trenton limestone and above by the Niagara 

 limestone. 



Under the title of "Hudson River group," Professor James Hall, describ- 

 ing the shales occurring between the Galena limestone and the Niagara 

 Limestone in [owa, mentions certain .shales on the Little Maquoketa river 

 which were referred to the Hudson Kiver group.§ It is stated that the 

 section is scarcely more than twenty live feet in thickness, ami that on the 

 opposite side of tie- river the entire thickness is probably less than 7") feet. 



In the second geologic survey of Iowa [| the classification adopted refers 

 the rocks described a- the Hudson River Bhales by Professor Hall to the 



•Am. .I"iir. Sri., vii I. 88, 1840, p, 90. 



t I'm--. Am \ idr. Set., rol 7, 18 ■. p, i 



logj of I .-nil. - . ■•, 1880, p| 

 . leol Survey Iowa, rol. i, i-e I, i - 

 Ki-|i-.ii oi-i.i. Surrey Iowa, rol, I, 1870, by < lhai lea \. White, p. I 



