144 Scientific Intelligence. 



scale, while they do indicate l'elative superposition locally have 

 only relative time value. 



Like the lines in the solar spectrum their position must be 

 known before they can be used as chronological marks. The 

 fossils on the other hand have an intrinsic time value, their char- 

 acters intimately connect them with what has preceded and what 

 follows them. Like the angle of refraction of the rays of light of 

 each color, each fossil has a normal time value. 



Fossils thus become the true criteria of the time scale ; but 

 the elements of the formation scale are local accumulations of 

 various kinds of sediments whose place in a geological time scale 

 is determinable only by fossils. The formations of one section 

 will overlap, and differ in composition and limits from those of 

 another section, — the time-scale should be a universal standard, 

 with no overlapping, with divisions, arbitrary it may be, but 

 never duplicated ; the marks of which are fossils, changing con- 

 stantly but in a definite order of sequence. 



In the case of the Catskill it was shown that within the limits 

 of the New York system, what is called the Catskill formation, 

 group or period is a geological formation, but is not either an 

 epoch or a period, and that Catskill is not an appropriate name 

 to apply to any division of the time-scale. Thus we may say of 

 the Catskill formation, that in the Genesee section in western 

 New York, the whole of Devonian time is recorded without any 

 trace of the Catskill formation, it is neither above, below or 

 within the Chemung. The whole of Devonian time transpires 

 and includes no such division as a Catskill epoch or period. One 

 hundred miles eastward, the section running through Cayuga 

 Lake, shows at the close of the Devonian, after the cessation of 

 the Chemung fauna, a Catskill formation of several hundred feet 

 thickness. Another hundred miles eastward, across Otsego Co., 

 the section contains (I) rocks of the Catskill formation for the 

 upper third of the upper Devonian, below them (2) a sparsely 

 fossiliferous zone of Chemung — probably its lower part, (3) a 

 modified Ithaca fauna, then (4) the Oneonta formation, which is 

 but a detached zone of the Catskill, next (5) a fauna intermediate 

 between that of the Ithaca and the typical Hamilton, underlain 

 by (6) the Hamilton formation of the middle Devonian. Still 

 further east, along the Hudson River valley, the Catskill forma- 

 tion occupies the whole of upper Devonian interval — and if we 

 go still farther east, in Maine we find rocks which are but the 

 extension of the same formation as the Catskill filling the whole 

 interval from the Oriskany to the Carboniferous; i. e. the upper, 

 middle and most of the lower Devonian system. 



In elaborating this dual nomenclature, it was proposed to con- 

 tinue the use, for the formation-scale of the present nomenclature 

 in the manner in which the newer work of the United States 

 Geological Survey is being defined, using geographical names in 

 combination with lithological terms for the nomenclature. For 

 the time-scale, the degree of precision increases in the opposite 



