44:6 G. K. Gilbert — Congress of Geologists. 



ing its application in other continents. It is adjusted to the 

 rock systems of Europe exclusively, and makes no provision 

 whatever for the systems of other parts of the earth. The 

 geologists of Wisconsin, for example, cannot use it without 

 calling the Keweenawan either Cambrian or Archaean. If they 

 were in dou'i>t which division should hold it, but inclined a 

 little one way or the other, they could express their qualified 

 opinion in the notation provided by the map committee; but 

 having attained an unqualified opinion that the terrane belongs 

 to neither of these two categories, they find no means for ex- 

 pressing their conclusions. The scheme cannot be applied to 

 the geology of India, of New Zealand, or of Australia, with- 

 out misrepresentation. It is not universal but local, and this 

 because it is founded on the fallacy of a world-wide unity of 

 geologic systems. 



So far as the geology of the world is concerned, it would be 

 better to adopt no convention at all as regards map colors, than 

 to adopt one carrying with it and promulgating a vicious classi- 

 fication. Uniformity is not worth purchasing at the price of 

 falsification. If the members of the Congress cannot agree 

 upon a plan having the flexibility demanded by the geologic 

 facts, it will be best to limit its action to the local problems in- 

 volved in the map of Europe. I believe, however, that the 

 necessary flexibility is attainable, and before proceeding to 

 further criticism of the committee scheme I will give the out- 

 lines of a plan which appears to me to combine the advantage 

 of flexibility with a number of other desirable qualities. 



The plan is founded on the universality of geologic time and 

 the diversity of local geologic histories as expressed in rock 

 systems. Geologic periods are arranged in linear order. Each 

 one adjoins the next and together they constitute continuous 

 geologic time, which we may conceive as represented by a 

 straight line. The stratigraphic systems of a country have 

 likewise an order of succession, and their arrangement is 

 linear. They are not always continuous one with another, but 

 the history recorded by the systems and the breaks between 

 them is continuous and may be represented by a straight line, 

 equal and parallel to that of geologic time. And so for each 

 country. A color scale which shall represent each and all of 

 these parallel lines must be itself linear and continuous, and, 

 fortunately, we have such a scale furnished us in the prismatic 

 spectrum. 



I propose, first, that the continuous prismatic spectrum be 

 adopted as the standard universal scale for continuous geologic 

 time. I propose, second, that the conventional time scale, 

 based on the geologic history of Europe, be complemented by 

 a color scale, prismatic but discontinuous. I would assign to 



