54 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



tern of correlation by means of the petrographic characters of the de- 

 posits was used in part by these geologists and formed the original 

 basis of the classification. In the field work the formations were dis- 

 tinguished by their petrographic features and were so defined. In 

 most cases local names were applied to them ; the geographic designa- 

 tion of the place where the particular formation was discovered, or was 

 found to be exposed in a good condition, was applied to the rock, and 

 as the surveys went on the name as applied was extended to the other 

 outcrops of what appeared to be the same stratum or series of strata. 

 This was all very well so long as no correlation was attempted, but as 

 soon as correlation of the several formations with those of other regions 

 was attempted the necessity of some other means of identification was 

 apparent. This means was recognized in the fossil contents, but in the 

 field the fossils were not studied, and could not be studied by the field 

 geologists. It was necessary to take them home and compare them 

 with other fossils from other parts of the country and world, and to de- 

 scribe them, and ascertain their range and distribution. All this re- 

 quired time and learning, which could not be attained at once by any 

 one of the geologists. This learning was the special province of the 

 paleontologist, and the wide knowledge requisite to correlate the 

 various strata of the New York system accurately with those of Great 

 Britain was, we may imagine, clearly recognized by Conrad before he 

 left the survey ; but, as we have learned since, many years of study 

 have not enabled geologists to establish with certainty the correlation 

 between the several faunas of the formations in New York and those 

 abroad. 



The great desideratum at that time, and for geologists at the present 

 time, is such a system of nomenclature and classification as shall ena- 

 ble the field geologist at once to record his observations correctly and 

 systematically, and to preserve the records of fossil contents which he 

 discovers for the careful detailed study of the paleontologist. The no- 

 menclature adopted in many cases by the New York geologists, which 

 has satisfied the demands of the progress of science, at least up to the 

 present time, is that which is based upon the simple practice of giving 

 a geographic name to a rock terrane, connecting it with the name of 

 the particular rock which is exhibited at the locality in which it out- 

 crops; for example, "Trenton limestone," "Oriskany sandstone," "Scho- 

 harie grit," " Genesee slate," although in the latter case slate is not ap- 

 propriate, because it is a false name, shale being the right name. 

 These several terms applied to definite rock masses located in particu- 

 lar regions in New York State, having their typical outcrops designated 

 by their names, can be applied with exactness at all times, and suggest 

 the progress of the science. Whenever wrongly applied to deposits out- 

 side the original region where discovered, new names can be easily sub- 

 stituted. 



The groupings of these separate formations, made without regard to 



