450 G. K. Gilbert — Congress of Geologists. 



The alphabet of colors for the prismatic scale will be the more 

 easily learned of the two. because it is orderly, and because 

 its order is already familiar in the spectrum. The committee's 

 scheme, however, has some old-fashioned mnemonic features 

 which the prismatic lacks. The green of the Cretaceous is con- 

 nected with green-sand, the red of volcanic rocks with fire, and 

 the rose of the Archaean with feldspar ; and the gray of the 

 Carboniferous mildly suggests the blackness of coal. 



In respect to facility of introduction the committee's scheme, 

 being essentially a compromise of existing color scales, has the 

 advantage that to most users it is not entirely novel. The pris- 

 matic scheme on the other hand has the advantage of being 

 orderly. It scientifically differentiates the functions of hues 

 and tones, and though each one of its colors may be different 

 from what the individual geologist has previously employed 

 for the indication of the same system, the order of the colors 

 is already familiar to him in another way. 



This closes my review of the various works undertaken by 

 the congress. Some of these have been favored, others op- 

 posed, and reasons have been given. But there is a general 

 consideration or criterion applicable to all, which has nearly 

 escaped mention, although it is* of preeminent importance. 

 When a matter is proposed for regulation by the congress, the 

 first question which should be asked is whether it falls within 

 the legitimate purview of a convention of geologists. It mani- 

 festly does not if it belongs to some other science rather than 

 to geology ; and objection has on this ground been made against 

 the regulation by our geologic congress of the nomenclatures 

 of paleontology and mineralogy. But not all geologic matters 

 even are properly subject to settlement by convention. This 

 is peculiarly the case with geologic facts. Science is distin- 

 guished from the earlier philosophies of mankind by the pecul- 

 iarity that it establishes its fundamental data by observation. 

 The old philosophies were founded largely upon assumptions, and 

 it was not deemed illogical — perhaps it was not illogical — to 

 appeal to the authority of an assemblage of experts for the 

 establishment of fundamental assumptions. But for science it 

 is not merely illogical, it is suicidal, to establish facts in any 

 other way than by observation. No vote of the most august 

 scientific body can possibly establish a fact, and no vote can 

 have any weight against a good observation. 



Now the entire science of geology, using the phrase in a 

 strict sense, is constituted by the aggregation and arrange- 

 ments of facts, and none of its results can be rendered more 

 true, or be more firmly established, or be prevented from yield- 

 ing to contradictory facts, by conventional agreement. A class- 



