THE 



JOURNAL OF GEOLOGY 



OCTOBER-NOVEMBER, iqo2 



CARTOGRAPHIC REPRESENTATION OF GEOLOGICAL 



FORMATIONS. 



As cartographic units, in the representation of geological 

 structure, the lithologic individual, the faunal stage and the 

 geological formation are commonly regarded as practically iden- 

 tical. In reality, they are fundamentally distinct from one 

 another. Moreover, these are not the only units which it is pos- 

 sible and practicable to map and bring out clearly the geological 

 structure of the area investigated. 



In the recent discussions on the units of geological mapping, 

 one of the most important fundamental factors appears to be 

 entirely overlooked. The two leading phases of the subject are 

 admirably summed up in the recent articles of Messrs. Willis 1 

 and Cross. 2 Although, at first glance, these authors seem to 

 present radically different views, they are not, actually, so far 

 apart in their contentions as they would have us believe. Mr. 

 Cross' conception is the more philosophical of the two ; it is 

 based on genetic grounds ; and it is the one which must finally 

 prevail, though the local criteria of discrimination may be diverse 

 in different cases. In actual practice, Mr. Willis' expressed idea 

 has the greater force and must be the one which must neces- 

 sarily long be followed. But the two conceptions are not 

 incompatible. In the practical application of the principles, the 

 final results become very nearly identical. 



To every one who has given the subject critical attention, it 



'Jour. Geol., Vol. IX, p. 557, 1901. -Ibid., Vol. X, p. 223, 1902. 



Vol. X, No. 7. 691 



