348 A SYMPOSIUM 



proposed scheme appears to lie in the disinclination of 

 most writers to make any distinction between a technical and 

 common usage of words. Terms that already have assumed 

 special meanings should be used only in a technical sense. For 

 expressing ideas in which a restricted meaning is not implied 

 there are many common terms. 



In geological classification a dual scheme has come to be so 

 universally recognized that it is difficult to imagine that any 

 other is possible. Yet, for local successions of strata a single 

 set of adjectives suffices to designate both the subdivisions of 

 time and those of substance. Hence, with five orders of terms 

 to denote the taxonomic rank of the name used — and these 

 appear to be all that will ever be useful in practical work — 

 we have : 



Orde 

 I 



2 



3 

 4 

 5 



The word group, sometimes used for the largest rock 

 division, is so thoroughly incorporated in our literature in a dif- 

 ferent sense, and is generally so loosely applied, that it seems 

 hopeless, and in fact very undesirable, to attempt to give it, at 

 this late day, a technical meaning. Moreover, it is far more 

 useful now, with its present indefinite application to any selected 

 number of beds or subdivisions, than it could possibly be in a 

 more restricted sense. Some other title should take its place 

 for technical purposes. It makes little difference what it is. Its 

 general adoption is the most important feature. Assemblage, 

 the name here given, is merely suggestive. It is somewhat 

 ponderous, but is expressive of the grand subdivisions. 



Stage is a word associated not with the idea of time, but of 

 place. It is, therefore, more properly applicable to the fourth 

 structural order, interchangeable, perhaps, with formation. But 

 the latter term may be extended without confusion to crystalline 



