1892.] PROSSER — THE GENESEE SECTION. 55 



terized by a Rhynchonella \^R. allegatiia Wms.] of large size * * * ^ 

 but it also contains frequent specimens of Spirifera disjuncta, linking 

 its fauna with the Chemung fauna below." (') 



*' The specimens [of Rhynclionella\ have been found in the ferru- 

 ginous sandstones underlying the conglomerate at Olean and Little 

 Genesee, in New York, and at Bradford, McKean County, Pa." C^) 



Again, "Above this conglomerate [Wolf creek] it is rare to find 

 any Chemung fossils, but they do not entirely cease till the second con- 

 glomerate of Genesee ' rock city,' the Olean conglomerate. Between 

 the two conglomerates are red and green, argillaceous shales (the 

 former sometimes bearing Chemung fossils), with flaggy, micaceous, 

 green shales and sandstones. The intervals between these two con- 

 glomerates may average about three hundred feet." (^) 



In the " conclusions " Professor Williams states that the flat peb- 

 ble (^^'olf creek) conglomerate is "at the top of the Chemung and 

 containing a fauna of decided Chemung type, which is distinct in some 

 features, but appears in the shales below. 



" These underlying shales in New York gradually run into genuine 

 Chemung rocks and fauna and cannot be discriminated from them by 

 any sharp line of distinction." (') 



In comparing the Allegany section with the authoritative one of 

 the Dennis well, near Bradford, Professor Williams regards stratum 

 No. 15 of the Dennis well as the equivalent of the Wolf creek con- 

 glomerate. (") The top of No. 15 is 330' below the base of the Olean 

 conglomerate and is in the Red Catskill of Ashburner, 167' above the 

 top of the Chemung. (") 



As a result of this comparison it will be noticed that at Bradford, 



(I.) Ibid., p. 87. 



(2.) Ibid., p. 88. 



(3.) Ibid., p. 89. 



(4.) Ibid., p. 103. In attempting to correlate the sandstones and shales between these two 

 conglomerates Professor Williams' opinion was sought, and October 7th, 1891, he wrote me the following 

 letter : 



" In a geological series running upward I give the name of the typical formation, as Chetnung, to 

 the rocks in which the typical fauna is contained, and include as of the same formation the rocks 

 above so long as they contain the same fauna. If the fauna changes, as in the case of the Little Gen- 

 esee conglomerate, I should give the formation a different name, and in case no typical Chemung 

 fauna occurred above I should speak of it as Upper Devonian, and not as a member of the Chemung 

 Period. 



" If the fauna changes from marine to fresh water or brackish water, in this case I would call the 

 fauna Catskill, even if it occurred below distinct beds of Chemung, with the marine fauna, possibly 

 giving some local name. It is the custom in this country and in Europe to consider Spiri/era dis- 

 juncta as confined to the Devonian, so that as long as it existed, 1 would apply the general name 

 Upper Devonian and Chemung." 



The Professor states that the above is a general rule which he follows in the correlation of the 

 Upper Devonian, consequently it is probably better to call the rocks between the two conglomer- 

 ates simply Upper Devonian. 



(5.) Ibid., p. 100 ; also, see p. 30. 



(6.) See the record of the Dennis well, 2d Geol. Surv. Penn., R, pp. 287-290, especially pp. 

 288, 200. 



