352 C. D. WALCOTT — THE TEEM "HUDSON RIVER GROUP. 



nois and Ohio, ami came into general use in the west. Borne geologists, how- 

 ever, preferred to use the term Lorraine, as proposed by Dr. Emmons, on 

 the ground of priority; and when, in 1877, Professor Hall stated that he 

 had been led into error in considering the rocks in the valley of the Hudson 

 as of primordial age, or older than those of the Lorraine and Cincinnati sec- 

 tions, and that be thought the term Hudson River group should he used in 

 geologic nomenclature, as it had specific value, the tendency to return to the 

 use of the name became more and more apparent among geologists. At 

 the same time, however, some geologists continued to use the name Lorraine; 

 others retained Cincinnati, and in Iowa, Maquoketa was used. 



Wishing to know more of the typical rocks included under the name 

 Hudson River group by Dr. Mather in his survey of the Hudson River 

 valley, I examined the sections both on the west and on the east sides of the 

 liver, with the result which I have already recounted. I then examined 

 and studied carefully the sections at Lorraine, on the Salmon river, and in 

 the Mohawk valley; and on returning from the field I read the descrip- 

 tions of the supposed equivalent series of rocks as found in Ohio and por- 

 tions of the Mississippi valley. 



The result of this study is the retention of the term Hudson* for the series 

 of strata between the Trenton limestone ami the superjacent Upper Silurian 

 rocks. The sections in the valley of the Hudson embrace all the strata be- 

 tween the Trenton limestone and the Upper Silurian, and include the Utica 

 Bhale formation, the intermediate silicious slate, as represented by the lower 

 portion of the Lorraine shales, and also the alternating sandstone and shales 

 of the Lorraine section. It is true that the typical fauna of the upper por- 

 tion of the series is not present in the valley of the Hudson bo far as known ■ 

 but we iiiu.-t recollect that stratigraphic geology preceded paleontology and 

 the identification of horizons by paleontologic evidence, and that when by 

 practically continuous stratigraphy a formation has Keen traced from one 

 area to another the name applied to the formation where first discovered 

 and named \sill hold good even though the rocks at the typical locality do 

 not contain the fauna u liich characterizes the horizon at some other locality. 

 The absence of a fauna in such a case does not injure the correlation : its 

 presence would of course strengthen the correlation, but in the case in hand 

 it do<- nut appear to be essential. 



In thus adopting the term Hudson for the entire Beries, I do not wish it 

 understood that I favor dropping the local name- Lorraine, Cincinnati, 

 Maquoketa, etc. The term Hudson is used in the generic Bense, to include 

 a group of formations that occur between the Trenton limestone horizon 



• ■■! the original Dame it dropped In order t" bring il Into harmony with the 

 n, Chazy, Niagara, etc.) tnd adapt ii to it- position • Ic term 



