THE DEVONIAN SECTION OF ITHACA, N. Y. 593 



hand. When the resurvey of the Watkins Glen quadrangle was 

 begun, I expected that these black bands would prove of value in 

 tracing and classifying the rock horizons from one quadrangle to 

 another. It was discovered, however, in the course of the survey, 

 that any particular mass of this fissile black shale does not retain 

 its peculiarities with sufficient uniformity to serve as a reliable mark 

 of a definite horizon. 



The same may be said of local thick-bedded sandstones ; they are 

 also, so far as thickness is concerned, confined to narrow local dis- 

 tribution. The mode of change in the structure is through a break- 

 ing-up of the thick sandstone bed, by increase of shaly bands in its 

 midst, reducing it to a mass of thin-bedded sandstone and shales. 

 When for a considerable thickness no sandstone bands are present, 

 the section appears as a mass of fissile shales; when the shale layers 

 diminish, the sandstone bands run together, and become beds of 

 sandstone separated irregularly by shale bands in which case the 

 sandstones become the conspicuous features in the outcrops. 



It was also discovered that the faunas are associated with par- 

 ticular classes of sediments; hence, where similar types of strata 

 appear the fossils are also ahke — irrespective of stratigraphic 

 position within the formation through which the same fauna ranges. 

 These are some of the reasons for discarding from the systematic 

 nomenclature all such subdivisions of the strata as are of local narrow 

 distribution. 



Subdivisions of the Nunda formation not recognized in the Watkins 

 Glen and Ithaca quadrangles. — Other names have been applied to 

 subdivisions of the formation els'ewhere where they are considered 

 to be of member or lentil value. They have been discarded when- 

 ever the definitions given them, hthologic or paleontologic, fail 

 to apply to any recognizable portions of the section in the Ithaca 

 region. 



According to the United States Geological Survey rules, it has 

 been considered illegitimate to continue to apply member and 

 lentil names to corresponding stratigraphic portions of a formation, 

 when the section ceases to exhibit the Hthologic or paleontologic 

 characters upon which discrimination of the members was based. 

 The formation name should be appHed, according to rule 4, "as 



