DUAL NOMENCLATURE. 1 49 



mark or distinguish the divisions one from another, as a scale it 

 is one and continuous, the parts or divisions of the scale come 

 up to each other and are in a regular succession, but they cannot, 

 from the nature of the scale itself, overlap or duplicate each 

 other. Uniformity in nomenclature, and definite well-known 

 standards and limits, and accepted means of recognizing each 

 division for universal use, are essential to the perfection of this 

 time-scale. In all geological literature only one name should 

 be applied to each subdivision of the time scale, and there 

 should be recognized for each of the grander divisions a prime 

 standard, in some particular place on the earth, whose marks 

 may be examined with closer and more minute discrimination as 

 the science develops in precision. Further, in each continent 

 we need separate standards which shall be compared as accu- 

 rately as possible with the prime standard, so that each conti- 

 nent may have its typical geological time-scale, in concrete form, 

 with which local formations may be corrected. 



The above applies, however, only to the time-scale; the list 

 of geological formations is a totally different thing; there is no 

 universal uniformity of geological formations ; to attempt to 

 apply a single set of names to them is always more or less to cramp 

 and distort the facts. Geological formations are local affairs, and 

 to restrict geological classification to a single formation scale is 

 to hide-bind the progress of science. There may be as many for- 

 mation scales as there are examined sections of stratified rocks, 

 and we know that all the marks by which a formation may be 

 defined constantly vary, so that the definition of a formation, 

 small or great, is not alike for any ten miles of its extent, and 

 often ten feet of extension will show clear marks of difference. 



Thus we see that there are two distinct sets of facts with 

 which the geologist has to deal, and the United States Geolog- 

 ical Survey has clearly recognized this truth in giving rules for 

 the definition and naming of geological formations, independent 

 of time relations, which are left for the more deliberate determi- 

 nation of the paleontologists. It is not, however, in the new 

 work so much as in the revision of old standards that the appli- 



