Association of American Geologists and Naturalists. 157 



and secondly, of a word or words descriptive of the ruling mineral 

 character of the rock ; and to these is appended, when we wish to 

 specify the type under which the formation is referred to, the name of 

 the district or place where it is so developed. Let me exemplify this 

 by one or two instances. The well characterized formation called in 

 the New York survey the Marcellus shales, is named by us the Post- 

 medidial older black slate, while the Genesee slate is called Postmedi- 

 dial newer black slate, and a member of the Clinton group of New 

 York, occuring there as a thin bed of brown and ponderous sandstone, 

 (seen on the Sequoit,) but expanded in Pennsylvania and Virginia into 

 an important mass having characteristic fossils and a maximum thickness 

 oi two hundred feet, we propose to call the Levant iron sandstone. 



The nomenclature here employed for the designation of the strata, 

 is recommended we conceive by several features of obvious utility. 

 Being a nomenclature based on considerations of geological time, it 

 suggests at once in the names themselves the relative ages of the differ- 

 ent strata, thus defining the fundamental relationship of succession in 

 tme i ^e only relationship between rocks which never varies. It has 

 thus the advantages of a numerical or ordinal designation, combined 

 with the descriptiveness which that has not. While it conveys the fixed 

 batons of time, it expresses the accidental or local character of each 

 formation, and what is of much more importance, it signifies under 

 what particular type any special stratum is referred to, by introducing 

 mto the name that of the district where the rock assumes the phases 

 seated of. Thus by the mere name assigned to each formation we 

 are remi nded of all its most essential attributes, its age, its region, and 

 1 s mineral composition ; or in other words, what place among the other 

 str *ta it occupies— in what district we are describing it, and what its 

 imposition is under its normal or typical development. One of the 

 most ob vious defects in any nomenclature is a want to ready adaptibility 

 t0 new or abnormal relations and conditions of the objects named, and 

 ,n l fos unfortunate rigidity in the terminology of some of the sciences 

 * e ttay discern a most influential barrier to their progress. In divising 

 * e system proposed, we have aimed at uniting the power of representing 

 { e fundamental or permanent relations of the objects named, and of 

 Piantly expressing their special deviations and gradations. In the 

 P e nomena of mineral and Palceontological deviations of type lie con- 

 ale d, we should remember, the very arcana of our science, secrets 

 u nc h interpreted will give us the only insight we can hope ever to 

 procure ^to the actual state of our earth's surface in periods long re- 



